Ocular therapeutic agent delivery devices and methods for making and using such devices

ABSTRACT

Ocular implant devices for the delivery of a therapeutic agent to an eye in a controlled and sustained manner. Dual mode and single mode drug delivery devices are illustrated and described. Implants suitable for subconjunctival placement are described. Implants suitable for intravitreal placement also are described. The invention also includes fabrication and implementation techniques associated with the unique ocular implant devices that are presented herein.

FIELD OF THE INVENTION

The present invention generally relates to local therapies for the eyeand, more particularly, to controlled-release ocular implant devices,including methods for making and using such devices, for delivery oftherapeutic agents to the eye.

BACKGROUND OF THE INVENTION

In the treatment of many diseases and disorders of the eye, andespecially in the case of degenerative or persistent conditions,implantable sustained-release delivery devices have been desired thatwould continuously administer a therapeutic agent to the eye for aprolonged period of time.

Local ocular implants of a wide variety of constructions and placementshave been proposed heretofore for dispensing a therapeutic drug to theeye.

For instance, U.S. Pat. No. 4,014,335 describes an ocular drug deliverydevice placed in the cul-de-sac between the sclera and lower eyelid foradministering the drug and acting as a reservoir. The ocular device ischaracterized therein as administering drug to the eye in a controlled,continuous dosage rate over a prolonged time. To accomplish this, theocular device comprises a three-layered laminate of polymeric materialsholding the drug in a central reservoir region of the laminate. The drugdiffuses from the reservoir through at least one of the polymeric layersof the laminate.

U.S. Pat. No. 5,773,021 describes bioadhesive ophthalmic inserts thatare placed in the conjunctival sac, in which the inserts are prepared byextrusion, thermoforming, or heat compression of a polymeric materialmatrix and the drug to be delivered. The polymeric matrix comprises awater-soluble biocompatible polymer, such as hydroxyalkyl celluloses,maltodextrins, chitosans, modified starches or polyvinyl alcohols; awater-insoluble biocompatible polymer such as an alkyl cellulose; andwhere applicable a bioadhesive polymer such as polyvinyl carboxylic acidtype polymers or certain bioadhesive polysaccharides or derivativesthereof. The ophthalmic inserts are characterized therein as intendedfor the prolonged and controlled release of a medicinal substance.

U.S. Pat. No. 5,773,019 describes a continuous release drug deliveryimplant which, among other mentioned places, can be mounted either onthe outer surface of the eye or within the eye. A drug core is coveredby a polymer coating layer that is permeable to the low solubility agentwithout being release rate limiting. Descriptions include a coating ofcyclosporine A (CsA) drug cores with one or multiple coatings ofpolyvinyl alcohol solution, followed by heating to 110, 104 or 120° C.,presumably to cross link and harden the coating(s) in place around thecore. Also described is a implant prepared by fixing a pellet directlyover a smaller hole formed in a silicone film, followed by a suturebeing placed around the pellet in a gapped relationship thereto, andthen the entire assembly is coated again with silicone to form theimplant. The ocular device is characterized therein as giving acontinuous release to an affected area, once implanted, and producinglong-term sustained tissue and vitreous levels at relatively lowconcentrations.

U.S. Pat. No. 5,378,475 describes a sustained-release implant forinsertion into the vitreous of the eye. The implant has a firstimpermeable coating, such as ethylene vinyl acetate, surrounding most,but not all, of a drug reservoir and a second permeable coating, such asa permeable crosslinked polyvinyl alcohol, disposed over the firstcoating including the region where the first coating does not cover thedrug reservoir, to provide a location through which the drug can diffuseout of the implant. The implant also has a tab which can be used tosuture the device in place in the eye. The implant devices are preparedby applying coating solutions, such as by dipping, spraying or brushing,of the various coating layers around the drug reservoir.

U.S. Pat. No. 5,725,493 describes an ocular implant device for providingdrugs to the vitreous cavity over a period of time. The drug reservoiris attached to the outside of the eye with a passageway permittingmedicament to enter the vitreous cavity of the eye. The above-listing ofpublications describing prior ocular implant systems is intended to beonly illustrative in nature, and not exhaustive.

Local ocular implants avoid the shortcomings and complications that canarise from systemic therapies of eye disorders. For instance, oraltherapies for the eye fail to provide sustained-release of the drug intothe eye. Instead, oral therapies often only result in negligible actualabsorption of the drug in the ocular tissues due to low bioavailabilityof the drug. Ocular drug levels following systemic administration ofdrugs is usually limited by the blood/ocular barriers (i.e., tightjunctions between the endothelial cells of the capillaries) limit drugsentering the eye via systemic circulation. In addition, variablegastrointestinal drug absorption and/or liver metabolism of themedications can lead to dose to dose and inter-individual variations invitreous drug levels. Moreover, adverse side effects have beenassociated with systemic administration of certain drugs to the eyes.

For instance, systemic treatments of the eye using the immune responsemodifier cyclosporine A (CsA) have the potential to cause nephrotoxicityor increase the risk of opportunistic infections, among other concerns.This is unfortunate since CsA is a recognized effective active agent fortreatment of a wide variety of eye diseases and indications, such asendogenous or anterior uveitis, corneal transplantation, Behcet'sdisease, vernal or ligneous keratoconjunctivitis, dry eye syndrome, andso forth. In addition, rejection of corneal allografts and stem cellgrafts occurs in up to 90% of patients when associated with risk factorssuch as corneal neovascularization. CsA has been identified as apossibly useful drug for reducing the failure rate of such surgicalprocedures for those patients. Thus, other feasible delivery routes forsuch drugs that can avoid such drawbacks associated with systemicdelivery are in demand.

Apart from implant therapies, other local administration routes for theeye have included topical delivery, such as ophthalmic drops and topicalointments containing the medicament. Tight junctions between cornealepithelial cells limit the intraocular penetration of eye drops andointments. Topical delivery to the eye surface via solutions orointments can in certain cases achieve limited, variable penetration ofthe anterior chamber of the eye. However, therapeutic levels of the drugare not achieved and sustained in the middle or back portions of theeye. This is a major drawback, as the back (posterior) chamber of theeye is a frequent site of inflammation or otherwise the site of actionwhere, ideally, ocular drug therapy should be targeted for manyindications.

Age-related macular degeneration (AMD) is a common disease associatedwith aging that gradually impairs sharp, central vision. There are twocommon forms of AMD: dry AMD and wet AMD. About ninety percent of thecases of AMD are the dry form, caused by aging and thinning of thetissues of the macula; a region in the center of the retina that allowspeople to see straight ahead and to make out fine details. Although onlyabout ten percent of people with AMD have the wet form, it poses a muchgreater threat to vision. With the wet form of the disease, rapidlygrowing abnormal blood vessels known as choroidal neovascular membranes(CNVM) develop beneath the macula, leaking fluid and blood that destroylight sensing cells and causing a blinding scar tissue, with resultantsevere loss of central vision. Wet AMD is the leading cause of legalblindness in the United States for people aged sixty-five or more withapproximately 25,000 new cases diagnosed each year in the Unites States.Ideally, treatments of the indication would include inducing aninhibitory effect on the choroidal neovascularization (CNV) associatedwith AMD. However, in that the macula is located at the back of the eye,treatment of CNVM by topical delivery of pharmacological agents to themacula tissues is not possible. Laser photocoagulation, photodynamictherapy, and surgical removal is currently used to treat CNVM.Unfortunately, the recurrence rate using such methods exceeds 50% withina year of therapy.

As an approach for circumventing the barriers encountered by localtopical delivery, local therapy route for the eye has involved directintravitreal injection of a treatment drug through the sclera (i.e., thespherical, collagen-rich outer covering of the eye). However, theintravitreal injection delivery route tends to result in a short halflife and rapid clearance, without sustained release capability beingattained. Consequently, daily injections are frequently required tomaintain therapeutic ocular drug levels, which is not practical for manypatients.

Given these drawbacks, the use of implant devices placed in or adjacentto the eye tissues to deliver therapeutic drugs thereto should offer agreat many advantages and opportunities over the rival therapy routes.Despite the variety of ocular implant devices which have been describedand used in the past, the full potential of the therapy route has notbeen realized. Among other things, prior ocular implant devices deliverthe drug to the eye tissues via a single mode of administration for agiven treatment, such as via slow constant rate infusion at low dosage.However, in many different clinical situations, such as with CNVM inAMD, this mode of drug administration might be a sub-optimal oculartherapy regimen.

Another problem exists with previous ocular implants, from aconstruction standpoint, insofar as preparation techniques thereof haverelied on covering the drug pellet or core with a permeable polymer bymulti-wet coating and drying approaches. Such wet coating approaches canraise product quality control issues such as an increased risk ofdelamination of the thinly applied coatings during subsequent dippings,as well as thickness variability of the polymer around the drug pelletsobtained during hardening. Additionally, increased production costs andtime from higher rejection rates and labor and an increased potentialfor device contamination from additional handling are known problemswith present implant technology.

Accordingly, this invention provides local treatment of a variety of eyediseases. The present invention also provides a method for the deliveryof pharmaceuticals to the eye to effectively treat eye disease, whilereducing or eliminating the systemic side effects of these drugs. Thisinvention also provides sustained-release ocular implants foradministration of therapeutic agents to the eye for prolonged periods oftime. Additionally, this invention provides multi-modalsustained-release ocular implants. The invention also provides methodsfor making ocular implants with reduced product variability. Theinvention also provides methods for making ocular implants well-suitedfor ocular treatment trials using animal models. Other advantages andbenefits of the present invention will be apparent from consideration ofthe present specification.

SUMMARY OF THE INVENTION

The present invention provides ocular implant devices for the deliveryof a therapeutic agent to an eye in a controlled manner. The inventionalso includes fabrication and implementation techniques associated withthe unique ocular implant devices that are presented herein.

In one embodiment of this invention, ocular implants are provided whichadminister a therapeutic drug to the eye according to dual mode releasekinetics during a single treatment regimen. For instance, an ocularimplant under this embodiment of this invention delivers drugcontinuously to the eye by initial delivery at a high release rate toeye tissues soon after placement of the implant in or near the eye, as afirst administration mode, followed by drug delivery via a continuous,sustained lower release rate thereafter, as a second administrationmode, and within the same treatment regimen using the same implantdevice. The delivery of drug is never interrupted during the regimen, asa smooth transition occurs in the changeover from the high to lowrelease rate modes of drug delivery during the regimen. In this manner,the delivery of drug by the implant is dual mode or dual action innature. Animal model studies have been performed, which are describedelsewhere herein, that confirm this dual mode performance capability inlocal eye therapies for several embodiments of implants of thisinvention. As a consequence, no intervention is needed betweeninitiation of the treatment, i.e., installing the ocular implant, anddiscontinuation of the treatment regimen, i.e., exhaustion of the drugreservoir after a prolonged period of time.

Although not desiring to be bound to any particular theory, a largeinitial dosage is delivered at a relatively high release rate to the eyetissues via an ocular implant according to one embodiment of the presentinvention in a manner effective to substantially saturate the eyecompartments, permitting an ensuing lower release rate, maintenancedosage delivered over a period of time by the same implant to moreeffectively reach the target site of treatment, even if located in aposterior chamber of the eye. A dual mode implant according to theembodiment of this invention provides the sustained-release of thetherapeutic agent for a prolonged period of time after the period ofhigh release kinetics.

For purposes of this application, the term ‘loading dose’ refers to arapid release phase of a pharmacological drug in a mammalian organism inwhich an initial high release rate of the drug is observed followed byexponential or nearly exponential decline or decay in the release rateas a function of time. The terminology ‘sustained dose’ refers to thephase during which release rates are substantially constant over aprolonged period of time, and consequently concentration of thetherapeutic agent in the eye tissues achieves a substantially steadystate value over that period of time. The terms ‘loading dose’ and‘sustained dose’ are used in connection with drug treatments of the eye,unless indicated otherwise. Moreover, from a pharmacological standpoint,the initial dosage delivered at a relatively high release rateconstitutes a loading dose, and the sustained lower release rate doseconstitutes a maintenance dosage, suitable for the effective treatmentof an eye disease, disorder, ailment or condition. The terms “dose” and“dosage” are used interchangeably herein.

The present invention embodies implants which can provide such dual mode(“dual action”) performance, or optionally other modes of therapy viamodified configurations thereof which are also described herein.

One aspect of the invention relates to “matrix” type implants, soreferenced occasionally herein for convenience sake as every embodimentof implant under this category at least includes a composite matrix ofpolymer and therapeutic agent dispersed therein.

In one embodiment of this aspect of the invention, an implant providestherapeutic agent to the eye, in which the implant includes:

(a) a composite material matrix layer including:

(i) a therapeutic agent, and

(ii) a polymeric matrix material into which the therapeutic agent isdispersed, including (1) a polymer permeable to the therapeutic agentand present as a bioerodible solid matrix structure, and (2) awater-soluble polymer having greater water solubility than the permeablepolymer, and

(b) optionally, a discrete solid core containing additional therapeuticagent, which is surrounded and covered by the composite material matrixlayer.

This matrix type implant configuration is particularly well-suited forsubconjunctival or intravitreal placement, but is not limited theretoand could be installed on or in other eye regions where convenient anduseful.

In a more specific embodiment, the composite material matrix layercomponent of the matrix type implant comprises about 5 to about 50 wt %permeable polymer, about 0.05 to about 90 wt % water-soluble polymer,and about 1 to about 50 wt % therapeutic agent. Preferably, thecomposite material matrix layer component comprises about 5 to about 20wt % permeable polymer, about 0.05 to about 20 wt % water-solublepolymer, and about 1 to about 50 wt % therapeutic agent. As fabricated,the implant is a solid structure.

In one preferred embodiment of the matrix type implant, the permeablepolymer is a superhydrolyzed polyvinyl alcohol (PVA), which permitsdiffusion of the therapeutic agent therethrough, and forms a slowlybioerodible solid structure, and the water-soluble polymer is apharmaceutical grade cellulose ether. Uncrosslinked superhydrolyzed PVAreleases the drug by surface erosion of the PVA and by diffusion of thedrug through the superhydrolyzed PVA. The rate of erosion of thesuperhydrolyzed PVA is sufficiently slow that the polymer material inthe implant will dissolve so that the therapeutic agent pellet (“drugpellet”), when included, will disintegrate only after an extended periodof time, such as months or even years, in order to provide a slowsustained delivery of drug.

In addition, the superhydrolyzed PVA is water permeable and permeable tothe therapeutic agent in a predictable manner upon saturation with bodyfluids, yet offers the advantage of undergoing very limited expansionwhen the implant is installed. The low wet expansion behavior ofsuperhydrolyzed PVA prevents the implant from being extruded, and alsopermits more predictable pharmacokinetic behavior of the device. Also,the superhydrolyzed polyvinyl alcohol used in the polymeric matrixmaterial is essentially noncrosslinked through its secondary hydroxylfunctionality, i.e., it is not heated to temperatures during preparationof the implant sufficient to induce a level of crosslinking whichimpairs its permeability to the therapeutic agent present in either theinner core or the composite material matrix layer. The superhydrolyzedPVA is slowly bioerodible and not rapidly water-soluble in body fluids,so that the inner core does not disintegrate soon after installation ofthe implant. For purposes of this invention, a superhydrolyzed polyvinylalcohol is a polyvinyl alcohol having at least 98.8 wt % hydrolysis,preferably at least 99.0 wt % hydrolysis, and most preferably at least99.3 wt % or more hydrolysis. Generally, the superhydrolyzed polyvinylalcohol for use in this invention generally have a weight averagemolecular weight of about 85,000 to about 150,000, and preferably about100,000 to about 145,000.

On the other hand, the separate water-soluble polymer included in thepolymeric matrix material provided in the matrix type implant preferablyis a nonionic cellulose ether polymer. The cellulose ether polymer usedgenerally has a weight average molecule weight of about 70,000 to about100,000, and preferably about 80,000 to about 90,000. The water-solublepolymer is used as a processing aid during preparation of the compositematerial matrix layer. Namely, it acts as a suspension and dispersionaid for introducing the therapeutic agent into an aqueous medium, andbefore admixture with the superhydrolyzed PVA ingredient, in a premixstep involved with fabricating the implant (discussed in more detailbelow). Examples of such cellulose ether compounds include hydroxyalkylcellulose materials, such as hydroxypropyl methyl cellulose (HPMC),hydroxypropyl cellulose (HPC), and hydroxyethyl cellulose (HEC). Ingeneral, the higher the proportion of cellulose ether present in thepolymeric matrix part of the matrix implant relative to the proportionof superhydrolyzed PVA, the more rapid the release of the therapeuticagent.

In one preferred embodiment of the matrix implant, a therapeutic agentis included in both the inner core or pellet and the exterior compositematerial matrix layer or cladding. This results in a dual mode releaseof the therapeutic agent or drug into the eye during a treatmentregimen. That is, a loading dose is initially delivered to the eye bythe matrix implant followed by a transition in the release rate,continuing uninterrupted drug delivery by the implant, down to arelatively steady maintenance dosage that is sustained over a prolongedperiod. Initially, the therapeutic agent is released both from thepolymer matrix and the inner core or pellet of this embodiment ofimplant, creating the rapid release rate of the loading dose. Once theconcentration of drug initially preloaded into the compositedrug/polymer matrix cladding material diffuses into the eye, themaintenance dosage of drug is derived at a relatively constant rate fromthe remainder of the drug diffusing from the inner core or pelletthrough the composite material matrix layer which surrounds the core.

Moreover, an added advantage of this embodiment is that this dual modetherapy can be achieved via subconjunctival implant placement for someeye treatments. Thus, a less invasive and simpler procedure that doesnot require piercing of the vitreous body is provided. Used as asubconjunctival implant, it can be placed behind the surface epitheliumwithin the subconjunctival space. It also is possible to install theseimplants at or near other specific sites on or within the eye, such asintravitreal, if desired or useful.

This matrix implant embodiment of the invention also can be deployed forsingle mode or single action therapy in the eye by omitting the solidcore or pellet of therapeutic agent, and using the composite materialmatrix layer alone, which is the same general construction as that usedin the dual mode device. The single mode matrix implant releases aloading dose for a short period of time (e.g., up to about 30 days), butdoes not provide a sustained maintenance dosage over a prolonged periodthereafter.

In an optional configuration, a portion of the outer surfaces of thematrix implant, such as one side of the composite material matrix layer,has a top coat provided that is a polymeric material that is impermeableto the therapeutic agent, such as polymethyl methacrylate (PMMA). Inthis way, the release rate of the matrix implant can be reduced in amanaged manner, if desired.

As another alternative embodiment of matrix implant according to thisinvention, poly(ethylene vinyl) acetate (EVA) control can be used in thepolymeric matrix material in lieu of the superhydrolyzed PVA. EVA isnonbiodegradable and permeable to water. In the same general manner asthe PVA-based matrix implants, the EVA-based matrix implants can providedual mode or single mode drug release depending on whether the drugpellet is included (dual mode, i.e., loading plus slow constant raterelease) or not (single mode, i.e. slow constant rate release only).

Both the dual mode and single mode variants of the matrix implants ofthis invention are well-tolerated and non-toxic to the patient orrecipient (i.e., a mammalian host—human or veterinary). In addition, thematrix implant design of this invention can be prepared by uniquemethodologies and selections of materials leading to and imparting theunique pharmacological performance properties present in the finisheddevices.

Among other eye therapies, the matrix implant of the present invention,such as when used in a subconjunctival placement, provides an effectivetreatment in corneal transplantation procedures to reduce rejectionrates. For example, an immune system modifier agent such as cyclosporinecan be delivered non-systemically to the eye, in order to reducerejection rates of corneal allografts. Alternatively, this implant canbe installed in the vitreous humor to deliver 2-methoxyestradiol(occasionally abbreviated herein as “2ME2”) for treatment of CNVM. Also,other drugs or drug cocktails can be delivered as desired andappropriate.

Another aspect of the invention relates to “reservoir” type implantswhich include a silicone-encapsulated reservoir containing therapeuticagent. The reservoir type implants of this invention are intraocular,and preferably intravitreous implants. The intraocular reservoirimplants are sustained-release devices which deliver therapeutic agentto the eye over a prolonged period of time.

The intraocular reservoir implant generally includes an inner corecomprising a therapeutic agent for the eye covered by, and radiallycentered within, a polymeric layer comprising a nondegradable materialpermeable to the therapeutic agent, as a subassembly, and an ocularattachment means affixed to an exterior surface of the polymeric layerof the subassembly. In a preferred embodiment of the invention, thenondegradable material is silicone.

Methodologies are used in this intraocular reservoir implantconfiguration which ensure that the silicone is degassed and that theinner core is well-centered, at least radially, within a polymercomprising silicone. This results in unhindered diffusion of the drugfrom the reservoir through the silicone, as air bubbles or pockets areeliminated which otherwise would not permit such diffusion. As a result,a controlled and predictable drug release rate can be obtained.Centrifugation is used in conjunction with a temporary thin walledtubular mold made of low adhesion plastic in a multi-step processeffective to degas the silicone encapsulating material and radiallycenter the drug core within a polymeric material before the polymericmaterial is fully hardened.

In one embodiment of preparing the intraocular reservoir implant, thesteps of the method generally include positioning a thin walled tubemade of low adhesion (releasable) plastic, such as apolytetrafluoroethylene tube, in a temporarily fixed upright positionwithin a centrifuge tube. A base made of hardened silicone, or apolymeric material having similar permeability, is then formed at thebottom section of the plastic tube, such as by introducing a curablesilicone fluid in the bottom of the microcentrifuge tube, positioning abottom section of plastic tube below the surface of the curable siliconefluid. This is done in a manner such that the silicone fluid infiltratesand fills a lower section of the plastic tube, and also fills the spacebetween the outer surface of the lower section of the plastic tube andthe inner facing wall of the centrifuge tube, followed by curing orhardening the silicone fluid to hold the plastic tube in an uprightposition within the microcentrifuge tube. Thereafter, a drug pellet, asthe drug core, is introduced into the plastic tube followed by additionof additional wet silicone into the plastic tube. The microcentrifugetube is centrifuged as needed to degas the additional silicone andplace, if necessary, the pellet on the silicone base positioned at thebottom of the plastic tubing. The additional curable silicone fluidadded inside the plastic tube is sufficient to completely immerse theexposed surfaces of the pellet as it rests on the hardened siliconebase. As needed, the drug pellet can be manually or mechanicallycentered on the silicone base using an insertable/retractable device orprobe to move and center the pellet as needed. The added silicone fluidis then cured inside the plastic tube. After the silicone is cured, theplastic tube is separated from the centrifuge tube, and the resultingsilicone-coated pellet reservoir type implant is in turn removed fromthe releasable plastic tube, as an implant subassembly. The reservoirimplant subassembly is joined to a means for attaching the implantsubassembly to intraocular tissues of the eye, such as a suture stub.

As an alternative to the suture stub, a silk mesh fabric can be embeddedin the silicone at one end of the reservoir type implant. This allows asuture to pass through the mesh embedded at the one end and the suturewill not scissor through the soft silicone since it is caught by themesh. The suture then passes through the edges of the scleral wound andis tied down.

The implant subassembly of the intraocular reservoir implants of theinvention provide a sustained, substantially constant delivery rate ofdrug over a prolonged period. The intraocular reservoir implants alsocan be modified to form dual mode release devices. For instance, in adual mode configuration, additional therapeutic agent could be dispersedin the silicone fluid before being used to encapsulate the drug core tocreate an initial higher release rate, or loading dose; alternatively,additional amounts of the drug could be dispersed in or attached as adiscrete inlay member onto a separate silicone adhesive used to attach asurface of the reservoir implant subassembly to a suture stub or thelike. Alternatively, multi-drug therapy could be provided by including adrug different from the drug core in the silicone surrounding the pelletor, in or on the silicone adhesive used to affix the implant reservoirsubassembly to the suture stub. In another embodiment, more than onereservoir implant subassembly, each comprising an encapsulated drugcore, can be attached to a common suture stub to provide concurrentdelivery of different drugs or additive introduction of a common drug.

As another dual mode embodiment of the reservoir implant, a circularwafer shaped pellet or tablet of therapeutic agent having a largerradial diameter than thickness can be fixed to a suture stub withsilicone adhesive; and a temperature-curable type silicone adhesive isthen used to form a coating bead around the periphery of thewafer-shaped pellet or tablet. Curing the bead of silicone coatingaround the tablet periphery can be delayed (preferably for about 18 to30 hours, more preferably approximately 24 hours), by keeping the coatedassembly at room temperature (e.g., 20-30° C.); thereafter peripheralbead coating of silicone ultimately becomes fully cured. The siliconeadhesive is in a constant state of curing but the process is notcomplete for 18-30 hours. The top surface of the tablet is coatedseparately with silicone before or after this “delay in cure” procedure,and cured. During the interim delay in cure period, some, but not all,of the therapeutic agent diffuses into the surrounding nonfully curedsilicone coating polymer at its periphery, which creates a high releaserate or loading dose when the implant is initially installed, followedby slow, lower dosage sustained release of the therapeutic agent.

Among other eye therapies, the intraocular reservoir implants of thepresent invention provide an effective treatment for sight-threateningeye diseases that include but are not limited to uveitis, age-relatedmacular degeneration, and glaucoma. Therapeutic agents useful in thisimplant design include, for example, 2-methoxyestradiol (2ME2) orangiogenesis compounds such as VEGF antagonists for treating CNVM; orcorticosteroids for treating uveitis, to name just a few examples.

The therapeutic agents and drugs deliverable by the implants of thisinvention generally are low solubility substances relative to thevarious polymeric matrices described herein, such that the agentsdiffuse from the drug core into and through the polymer material, whensaturated with body fluids, in a continuous, controlled manner.

The therapeutic agents and drugs that can be delivered by the implantsof this invention include, for example, antibiotic agents, antibacterialagents, antiviral agents, anti-glaucoma agents, antiallergenic agents,anti-inflammatory agents, anti-angiogenesis compounds, antiproliferativeagents, immune system modifying agents, anti-cancer agents, antisenseagents, antimycotic agents, miotic agents, anticholinesterase agents,mydriatic agents, differentiation modulator agents, sympathomimeticagents, anaesthetic agents, vasoconstrictive agents, vasodilatoryagents, decongestants, cell transport/mobility impending agents,polypeptides and protein agents, polycations, polyanions, steroidalagents, carbonic anhydride inhibitor agents, and lubricating agents, andthe like singly or in combinations thereof.

In these and other ways described below, the inventive implants offer amyriad of advantages, improvements, benefits, and therapeuticopportunities. The inventive implants are highly versatile and can betailored to enhance the delivery regimen both in terms of administrationmode(s) and type(s) of drugs delivered. The implants of this inventionpermit continuous release of therapeutic agents into the eye over aspecified period of time, which can be weeks, months, or even years asdesired. As another advantage, the inventive implant systems of thisinvention require intervention only for initiation and termination ofthe therapy (i.e., removal of the implant). Patient compliance issuesduring a regimen are eliminated. The time-dependent delivery of one ormore drugs to the eye by this invention makes it possible to maximizethe pharmacological and physiological effects of the eye treatment. Theinventive implants have human and veterinary applicability.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, benefits, and advantages of the present invention willbecome apparent from the following detail description of preferredembodiments of the invention with reference to the drawings.

FIG. 1 is enlarged view of a sustained release, subconjunctival matrixsingle mode implant device according to an embodiment of the invention.

FIG. 2A is enlarged view of a sustained release, subconjunctival matrixdual mode implant device according to an embodiment of the invention, inwhich a drug pellet is surrounded by a composite material matrix layerincluding polymeric material and a dispersion therein of additionaldrug.

FIG. 2B is a view of the sustained release, subconjunctival matrix dualmode implant device similar to the one shown in FIG. 2A, including aview of the drug pellet surrounded by the polymeric material anddispersed additional drug, and an optional eye attachment (suture stub).The cross-section shows the relationship of the drug pellet to thesurrounding polymer coating.

FIG. 3A schematically illustrates the delivery of a loading dose by asubconjunctival matrix dual mode implant of this invention into thesurrounding tissues and vitreous cavity.

FIG. 3B schematically illustrates delivery of a maintenance dosage bythe subconjunctival matrix dual mode implant shown in FIG. 3A,subsequent to delivery of the loading dose.

FIG. 4A graphically illustrates the delivery of a delivery of a loadingdosage according to a subconjunctival matrix single mode implant of thisinvention described in Example 4 herein.

FIG. 4B graphically illustrates the delivery of a loading andmaintenance dosage according to a subconjunctival matrix dual modeimplant of this invention described in Example 4 herein.

FIG. 5 graphically illustrates the effect of surface area and drugconcentration on release rates for a subconjunctival matrix single modeimplant of this invention.

FIG. 6 schematically illustrates the placement in the eye of anintraocular matrix implant according to another embodiment of thisinvention.

FIG. 7 is enlarged view, in cross-section, of a sustained releaseintraocular implant device according to another embodiment of theinvention a drug pellet surrounded by a permeable polymeric materialincluding optional additional drug, and an eye attachment means.

FIGS. 8A-I schematically depicts an enlarged view of process stepsassociated with making a reservoir implant subassembly according toanother embodiment of this invention.

FIGS. 9A-C depicts top, perspective, and front views, respectively, of areservoir implant (subassembly) according to a reservoir type implant ofthis invention.

FIGS. 10A-D schematically depict an enlarged view of diffusion oftherapeutic agent into an uncured silicone bead surrounding a drugpellet at different time intervals (0 min., 30 min., 2 hr., and 24 hr.,respectively) in a step associated with the making of a reservoirimplant according to a “delay in cure” technique of yet anotherembodiment of this invention.

FIG. 10E is a graphical illustration of in vitro loading doses in PBSachieved with 2ME2 reservoir implants of the type described inconnection with FIGS. 10A-H herein, as a function of the delay in curetime.

FIG. 11A schematically illustrates the delivery of a loading dose by anintravitreal reservoir dual-mode implant of this invention, which hasbeen placed in an eye as shown in FIG. 11C.

FIG. 11B schematically illustrates delivery of a maintenance dosage bythe intravitreal reservoir dual mode implant shown in FIG. 11A,subsequent to delivery of the loading dose.

FIG. 12A schematically illustrates an intravitreal reservoir single modeimplant according to an embodiment of the invention.

FIG. 12B schematically illustrates a dual mode intravitreal reservoirimplant according to an embodiment of the invention, includingtherapeutic agent in the silicone surrounding the drug pellet.

FIG. 12C schematically illustrates an intravitreal reservoir dual modeimplant according to an embodiment of the invention, includingtherapeutic agent in a silicone adhesive used to attach the reservoirimplant subassembly to the suture stub.

FIG. 12D schematically illustrates an intravitreal reservoir dual modeimplant according to an embodiment of the invention, includingtherapeutic agent in an inlay attached to a silicone adhesive used toattach the reservoir implant subassembly to the suture stub.

FIG. 12E schematically illustrates a double-barreled intravitrealreservoir implant configuration according to an embodiment of theinvention.

FIG. 13 graphically shows ocular tissue levels of a drug (CsA) atdifferent locations as delivered by a dual mode matrix implant of thisinvention implanted in the subconjunctival space, as described inExample 4.

FIG. 14 graphically shows the average in vitro release rate of a drug(2ME2) over time as delivered by a matrix implant of this inventionsuitable for placement in the vitreous, as described in Example 5.

FIG. 15 graphically illustrates the in vitro release rates of a drug(2ME2) according to reservoir implants of this invention that varies thepolymer thickness surrounding the drug pellet, as described in Example 6herein.

FIG. 16 is a table of the 2ME2 in vitro release rates observed for theintravitreal reservoir dual mode implant studies described in Example 6herein.

FIG. 17 graphically illustrates the levels of 2ME2 in the aqueous humor,vitreous humor and blood in rabbits at one and three months afterreceiving an intravitreal reservoir dual mode implant according to theinvention, as described in Example 7.

FIG. 18 graphically illustrates the release rates of triamcinoloneacetonide (TAAC) according to an embodiment of the invention and acomparison implant in a rat model of induced CNVM, as described inExample 8.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the featuresshown in the figures may be enlarged relative to other elements tobetter illustrate and/or facilitate the discussion herein of theembodiments of the invention. Features in the various figures identifiedwith the same reference numerals represent like features, unlessindicated otherwise.

DETAILED DESCRIPTION OF THE INVENTION

Matrix Implants:

Referring now to the figures, and in particular to FIG. 1, a sustainedrelease, matrix single mode implant device 10 of the invention is showncomprised of a single composite material matrix layer containing adispersion of a therapeutic agent, seen as white particles 12 in thefigure, and a polymeric matrix material 14 into which the therapeuticagent is dispersed. The polymeric matrix includes a polymer permeable tothe therapeutic agent and present as a bioerodible solid matrixstructure, and a water-soluble polymer having greater water solubilitythan the permeable polymer.

This implant configuration provides a single-mode, single action therapyin the eye in which a loading dose of drug is released.

Referring now to FIG. 2A, a modified variant of the matrix implant shownin FIG. 1, is illustrated, which provides dual mode (dual action) drugdelivery to an eye. In this implant 20, a drug core or pellet embeddedand encapsulated within a composite material matrix layer 22, 24 havingthe composition described above for implant 10. The composite materialmatrix layer includes a flat base portion 22 upon which the bottom ofthe drug pellet rests, and an upraised portion 24 which conformablymakes intimate physical contact with the top and side surfaces of thedrug pellet. The drug pellet 26 is not visible in FIG. 2A. FIG. 2Billustrates the embedded drug pellet 26, and an optional suture stub 28that can be used to attach the implant 20 to eye or other nearby tissueif desired or useful.

In this way, and as illustrated in FIGS. 3A and 3B, therapeutic agent isincluded in both an inner core or drug reservoir and as dispersed in theexterior composite material matrix layer or cladding of implant 20. Thisresults in dual mode or bimodal release of the therapeutic agent intothe eye 301 during a treatment regimen. That is, a loading dosage isinitially delivered by the conjunctival implant (FIG. 3A), followed by atransition in the release rate, during continuing uninterrupted drugdelivery by the implant, down to a relatively steady lower maintenancedosage 32 that is sustained over a prolonged period (FIG. 3B).

FIGS. 4A-B, based on data developed in the studies described in Example4 infra, graphically show the difference in the single mode matriximplant (FIG. 1) performance as compared to that of the dual mode matriximplant (FIG. 2A) which further includes a drug pellet core.

For the dual mode matrix implant, the therapeutic agent initially isreleased both from the polymer matrix and the inner core reservoir ofthis embodiment of the subconjunctival implant, creating the loadingdosage. Once the concentration of drug initially preloaded into thecomposite cladding material diffuses out into the eye, the maintenancedosage of drug is derived at a relatively constant rate from theremainder of the drug diffusing from the inner core through thecomposite material.

As to the materials used in constructing the matrix implants, thefollowing considerations are important. The composite material matrixlayer or member (22, 24) includes at least, and preferably predominantlyor exclusively, the following three ingredients: (1) a drug permeablepolymer, (2) a water soluble polymer, and (3) a dispersed therapeuticagent.

The permeable polymer preferably is superhydrolyzed polyvinyl alcohol.The permeable polymer is imperforate; i.e., it is not microporous. Thus,the drug or therapeutic agent passes through it by diffusion process.For purposes of this invention, a superhydrolyzed polyvinyl alcoholmeans a polyvinyl alcohol of at least 98.8 wt % hydrolysis, preferablyat least 99.0 wt % hydrolysis, and more preferably 99.3 wt % or morehydrolysis. Superhydrolyzed PVA is obtained in granular powder form fromAir Products and Chemicals, Inc., Allentown, Pa., U.S.A., as Airvol 125.Airvol 125 has at least 99.3 wt % hydrolysis, and intermediateviscosities of 28-32 cps and a pH of 5.5-7.5. The superhydrolyzed PVAthat can be used in this invention generally has a weight averagemolecular weight of about 85,000-150,000, and preferably about 100,000to about 145,000. Additional information on superhydrolyzed PVA isprovided at CAS No. 900289-5. Other suitable superhydrolyzed PVAproducts, include Airvol 165, also available from Air Products andChemicals, Inc., Allentown, Pa., U.S.A.

Superhydrolyzed PVA provides the requisite functionalities of permittingdiffusion of the therapeutic agent while forming a slowly bioerodiblestructure in the composite material matrix layer or member (22, 24) ofthe implant. The rate of erosion of the superhydrolyzed PVA issufficiently slow that a slow sustained delivery of drug, such as manymonths or even years, can be obtained as desired.

In addition, the low wet expansion behavior of superhydrolyzed PVAprevents the implant from being extruded from its position within ornear the eye, and also permits more predictable pharmacokinetic modelingbehavior of the device. For example, once the subconjunctival matriximplants of this invention are implanted in the subconjunctival space(e.g., in a rabbit), after 3-4 weeks, the edges of the matrix implantsconstructed with superhydrolyzed PVA have been observed to soften as thesurface of the polymer hydrates which decreases the risk that it willextrude (i.e., a sharp edge under the conjunctiva tends to catch the lidwhen it blinks, and this would undesirably move the implant anteriorlyand increase the risk it will extrude at the corneal limbus). Also, thesuperhydrolyzed PVA totally conforms to the globe of the eye and isadherent to the sclera after 3-4 weeks.

For bulkier implants (e.g. dual mode implants with large drug pellets)that are at higher risk of extrusion, one or two sutures can be placedthrough the edges of the implant to secure the implant to the sclera.

Also, the superhydrolyzed polyvinyl alcohol used in the polymeric matrixis essentially noncrosslinked through its secondary hydroxylfunctionality, i.e., it is not heated to temperatures during preparationof the implant sufficient to induce a level of crosslinking whichimpairs its permeability to the therapeutic agent present in either theinner core or the composite matrix material.

Heating the matrix implants at temperatures >100° C. for 3-8 hours willencourage PVA crosslinking and this may be desirable when attempting toreduce drug release rates from a particular implant.

The separate water-soluble polymer included in the polymeric matrixmaterial is a nonionic cellulose ether. Among other things, acts as asuspension and dispersion aid for the therapeutic agent in premix stepinvolved with fabricating the implant. Examples of such cellulose etherinclude hydroxyalkyl cellulose materials, such as hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), and methylcellulose(MC). HPMC can be obtained as METHOCEL from Dow Chemical (e.g., METHOCELE4M). METHOCEL is cellulosic in nature. It is dissolvable in the sametemperature ranges as superhydrolyzed PVA. The preferred hydroxypropylmethyl cellulose has a weight average molecular weight of about 70,000to about 100,000, preferably about 80,000 to about 90,000, and morepreferably about 85,000.

In that many useful therapeutic agents for ocular treatments arehydrophobic or lipophilic in nature, the present invention provides aprocessing strategy effective to uniformly disperse and maintain asuspension of such active agents and compounds in an aqueous medium inthe preparation of the matrix implants. To accomplish this, the methodfor preparing the composite material matrix layer component of thematrix implants includes a step of separately mixing and dispersing thetherapeutic agent to be incorporated in the composite (cladding)material first with cellulose ether and the like, which acts as adispersing or emulsifying aid to permit an emulsion-like suspension oftherapeutic agent in an aqueous fluid. Generally, this premixture willinvolve preparing an aqueous emulsion or suspension containing a mixtureof drug and an amount of cellulose ether effective to provide theabovementioned processing aid effects needed. This preliminarydispersion and suspension of the therapeutic agent using the celluloseether is done in the absence of the superhydrolyzed PVA and withoutheating. The premixture generally comprises the drug in a range amountof about 1.5% to about 80% and the cellulose ether in a range amount ofabout 0.05% to about 95%, on a dry weight basis.

In general, the premixture is not heated. An occasional drug needs70-110° C. to help the dispersion of the drug in the premixture.

Thereafter, the separately prepared emulsion or suspension of drug anddispersing aid polymer then is combined and mixed effectively andthoroughly with an aqueous solution of the superhydrolyzed PVAingredient. The superhydrolyzed PVA solution generally contains about 5to about 50 wt % of the superhydrolyzed PVA. Higher concentrationsolutions of superhydrolyzed PVA are more difficult to work with due toincreased viscosities. To optimize the drug suspension when using highconcentrations of PVA, preferably small volumes are prepared of the PVAsolution with frequent stirring under mild (noncrosslinking) heat.

The superhydrolyzed PVA solution can be combined with the celluloseether/drug mixture with a spatula or other suitable manual mixinginstruments. However, for more highly viscous suspensions, a blender maybe desirable. As such a blender, a MiniContainer is adapted to theblender to hold small volumes, where the blender is a Laboratory Blender(Model 51BL30), operated at speeds of 18,000 RPM (low) or 22,000 RPM(high) as needed. The Mini Container (MMGC1) was stainless steel andheld 12-37 ml, and was obtained from Waring Factory Service Center,Torrington, Conn. To add the materials to a blender, a bottom of theassay tube containing the PVA/METHOCEL/drug mixture is cut with a razorblade and the contents poured into the blender. In one method, themixture is blended at high speed (22K RPM) for up to 5 minutes, and theblended contents are then poured into a 50 ml assay tube and centrifugefor 2 minutes at 1-4k RPM to degas it.

In this way, an overall homogenous premixture can be provided for thecomposite material matrix layer that includes the three abovementionedingredients.

When describing the components of the PVA/cellulose ether/drug mixture,the PVA is expressed as a wt % of the PVA/water solution, e.g., 50 gramsof PVA in 100 ml of water is a 50% PVA solution. However, the othercomponents, i.e., the drug and cellulose ether, weights are expressed asthe % of the total dry weight of the PVA/cellulose ether/drug mixture.The combined drug/cellulose ether premixture and PVA solution generallyhas a composition of about 5 wt % to about 50 wt % superhydrolzyed PVA,about 0.05 wt % to about 90 wt % cellulose ether, about 1 to about 50 wt% drug. More preferably, the composite material matrix layer comprisesabout 5 to about 20 wt % superhydrolyzed PVA, about 0.05 to about 20 wt% cellulose ether, and about 1 to about 50 wt % therapeutic agent.

The homogenous premixture including the three above-mentionedingredients, then is formed into a sheet-like coating on a flatreleasable surface, or is injected between two releasable plates (e.g.glass) to provide a uniform desired thickness, and dried at roomtemperature and without application of heat (i.e., preferably at lessthan about 30° C.). Pieces of the dried uncrosslinked material are cutafter drying from the sheet in the profiles desired for the matriximplant. At this point, a single-mode version of the implant (FIG. 1)has been manufactured. Other implant shapes, such as a curvilineardesign, can be easily fabricated to conform to the curvature of thecornea, which may be helpful for corneal or stem-cell grafttransplantation and ocular inflammatory diseases. The dried matriximplant is uncrosslinked so that it is bioerodible.

For lower concentrations of PVA in the composition of matrix implants,such as less than about 15 wt %, the homogenous drug/cellulose ether/PVAmixture can be poured out onto a glass plate and this will flatten outon its own upon drying without the need for compression via a top plate.Alternatively, the mixture can be compressed between two glass plates tofurther ensure uniform thickness. The top glass plate can be removedwithout damaging the drug/cellulose ether/PVA composite by cooling thelay-up before its removal. One glass plate (top one) is removed aftercooling, and the other is left so that the PVA has a place to dry. Thesurface tension of the PVA generally keeps it adhered to the bottomglass plate so that it dries as a flat sheet. If both glass plates areremoved simultaneously after the cooling step, the PVA curls up and isnot usable. Where PVA concentrations higher than about 15% are used inmaking a matrix implant, such as about 50 wt % PVA, the sandwich ordouble glass plate technique preferably is used to help flatten out thesurface of the coating before it dries.

For preparation of dual mode matrix implants (FIG. 2A), a modifiedprocess is required to introduce and embed the inner drug core. The drugcore is a self-supporting solid or semi-solid part containing the drug,and has any convenient shape conducive for the making of sealingcoverage thereon by the composite material. For instance, the core canbe formed as a cylindrical-shaped pellet of the drug alone, or incombination with a pharmaceutically acceptable carrier. In any event,the dual-mode implant is assembled by depositing the drug core, such asdrug pellet or tablet, on the surface of a freshly prepared and coatedlayer of the composite material while still semi-flowable; the pellet isthen tapped or pushed with light force on its upper surface, such by useof an elongated tipped surgical device (e.g., a triple-0 Bowman probe),so as to submerge and embed it completely within and in contact with thepolymeric coating layer; finally, the polymeric material is hardened orcured around the pellet (generally at room temperature) to fix it inposition. The polymeric coating layer thickness is selected to adequateto permit complete encapsulation of the drug pellet. The submerging ofthe drug pellets into the wet, non-fully dried PVA slabs according tothis invention avoids tendencies of alternate approaches involvingmultiple dip and dry coat applications that tend to delaminate in use,thereby dramatically altering the drug release rates. Also, when drugpellets are embedded in a matrix with high PVA concentrations to makedual mode implants, this preferably is done by embedding them at theedges where the two glass plates come together and the polymer isexposed.

As seen in FIG. 2A, when a drug pellet having a rounded tablet shape isused, the matrix implant resulting from drying the above-mentionedmatrix coating layer containing the pellet has a saucer like shape witha flat surface on one side, and a hat shape on the opposite side, wherethe drug core is completely and physically intimately covered by apolymer coating including dispersed drug, without any entrapped airpockets or air spaces inside the implant. Depending on the type ofmammal intended for treatment with this implant, the purpose of theocular treatment, and the type of drug and polymer coating material, thedrug pellet cores generally range in diameter from about 1 mm to about 5mm and about 1.0 to about 2.5 mm in thickness, and the thickness of thepolymeric coating can range from about 0.01 mm to 1.0 mm (as measuredfrom a pellet surface to the outer surface of the polymeric layer). Inthe case of the single-mode matrix implants, the thickness of thehomogenous wafer-shaped polymeric material generally ranges from about0.1 mm to 2 mm, and the wafer has opposite flat surfaces.

Adjusting the loading dose in the matrix implant generally can be doneby changing the relative proportions of superhydrolyzed PVA, celluloseether, and drug in the matrix component. The maintenance dose deliveredby the dual mode matrix implants can be adjusted by changing the surfacearea of release (i.e., generally by altering the geometry and mass ofthe compressed drug pellet).

For instance, for a more rapid release rate in the matrix implant, ahigher proportion of the cellulose ether can be used relative to theproportion of superhydrolyzed PVA. If the mixture is predominantlycellulose ether, however, the loading dose generally lasts for only 24hours maximum. In that situation, during fabrication of the implant, thepellet is precoated with 15% uncrosslinked PVA (e.g., Airvol 125) anddried, before the coated pellet is embedded within the wet polymericcoating slab. In this way, when the cellulose ether rapidly dissolves,the pellet still holds together.

Other than the mixing proportions of the ingredients, factors affectingthe release rate in the matrix implants include: the permeability of thedrug in the matrix polymers; the drug concentration in the laminatelayer and in the embedded pellet; the surface area of the pellet; theamount of surface of the matrix polymeric layer disposed on the eye. Theeffect of the surface area and drug concentration on the release ratesof single mode matrix implants can be seen in FIG. 5.

Also, a slightly modified superhydrolyzed PVA polymer can be used tomodify the quantity and duration of the loading dose. For example, usingprogressively higher amounts of gamma radiation and/or heat exposure,can crosslink the PVA and reduce the implant release rate. Chemicalcuring agents or catalysts are generally not employed since the extentof cross-linking becomes to extensive and the loading dose drug releasecapability can be lost. If radiation, thermal or chemical crosslinkingis too extensive, the PVA will have inadequate permeability to the drugfor the implant to function effectively.

In another embodiment of the matrix implant, high (about 40 to about50%) superhydrolyzed PVA concentration polymeric matrices are provided.Small volumes (e.g., 3 ml or less) are advantageous when working withhigh concentrations of PVA to optimize the drug suspension in thematrix. After these matrices are made into dried sheets, 1×1×2 mmrectangular pieces can be cut from the sheet, each representing amicroimplant, for placement into animal eyes with smaller vitreousvolumes (e.g. mouse, rat, or rabbit). Each microimplant has drugdispersed as in the single mode matrix implant described above. Theadvantage of high concentrations of superhydrolyzed PVA is there isnegligible expansion of the implant if superhydrolyzed PVA (such asAirvol 125) is used. This lack of expansion is critical when placingthese microimplants in small eyes since they are less likely to damagethe lens and retina. These microimplants are useful for releasing drugsin the vitreous cavity to assess their efficacy in animal models ofdisease. These microimplants can also be employed as inlays that attachto reservoir implants, as described elsewhere herein. These inlaysattached to the reservoir implants can be employed for animal models aswell as in humans that require an intravitreal implant.

As mentioned above, where PVA concentrations higher than about 10 toabout 15 wt % are used in making a matrix implant, such as about 50 wt %PVA, the sandwich glass plate technique is preferably used to helpflatten out this highly viscous matrix. Subsequent cooling and removalof the top plate, enables the matrix to have uniform thickness upondrying.

In another embodiment, the matrix implant can be assembled with a suturestub to which the implant is attached. Suture stubs are used primarilyfor holding implants, whether of the matrix type or reservoir typedescribed elsewhere herein, in the vitreous cavity or beneath thesclera. Thus, the stubs generally are not biodegradable.

The suture stub can be formed of a biocompatible, aqueous-insolublepolymer, such as crosslinked PVA. The suture stubs can be made, forexample, using non-super hydrolyzed, high viscosity (62-72 cPs)polyvinyl alcohol (hydrolysis <99%) to increase bonding to hydrophobicsurfaces. A suitable non-super hydrolyzed, high viscosity polyvinylalcohol for use in making the suture stubs includes, for example, Airvol350 obtainable from Air Products and Chemicals, Inc., Allentown, Pa.,U.S.A. The polyvinyl alcohol is thermally crosslinked. The act ofheating with or without radiation generally crosslinks the PVAsufficiently that the addition of a chemical crosslinker is notnecessary. Optionally, a chemical crosslinker can be used while the PVAis dissolving in solution, i.e., before it is dried into a sheet, when amore rigid suture stub is required, for example, when larger implantsneed to be secured in the vitreous cavity. In this situation, the PVA iscured into the desired suture stub dimensions including previously addedconventional chemical crosslinking agents for that purpose, andpreferably those that are non-formaldehyde based crosslinking agent areused. These optional chemical crosslinkers include certain aldehydessuch as glyoxal, glutaraldehyde, hydroxyadipaldehyde, and salts ofmultivalent anions such as zirconium ammonium carbonates. For thepurpose of reducing the potential for ocular toxicity, anon-formaldehyde based crosslinking agent is preferred. Examples ofsuitable crosslinkers in this regard include Polycup 172 (1-4% d/d;Hercules, Inc.), which is a water soluble polyamide-epichlorohydrin-typeresin, and Bacote-20 (2-10% d/d; Magneium Elektron, Ltd.), a zirconiumammonium carbonate salt. To prevent dissolution, the stubs are heated atabout 130 to about 150° C. for about 5 to about 10 hours before use inthe presence of a dispersed crosslinker. A silicone adhesive, such asMED1-4213 silicone adhesive (NuSil, Carpinteria, Calif.) can be used tobond the implants to the suture stub.

In another configuration, a portion of the outer surfaces of theimplant, such as one side of the composite material matrix layer, has apolymer top coat that is impermeable to the therapeutic agent, such aspolymethyl methacrylate (PMMA). PMMA, such as obtained from Sigma, canbe prepared by dissolution of 1 g PMMA/10 ml acetone with stirring forabout 12 hours. One side or a portion of the implant can be immersed inthe resulting PMMA (e.g., three times over 30 minutes) and then dried(without heating). In this way, the release rate of the implant can bemodified (viz., reduced), as desired.

As another alternative embodiment of the invention, poly(ethylene vinyl)acetate (EVA) is used in the polymeric matrix material in lieu of thesuperhydrolyzed PVA, all other things essentially the same in theconstruction. This provides an optional dual mode implant structuregiving a loading dose followed by sustained slow release of drug. TheEVA is non-bioerodible.

These single mode and dual mode implant configurations are particularlywell-suited for subconjunctival placement, but are not limited theretoand could be installed on or in other eye regions where convenient anduseful, such as intravitreal placement using a suture stub. Forinstance, FIG. 6 is a schematic representation of a 2ME2-containingintraocular matrix implant 61 in an eye 63.

In administration, the subconjunctival matrix implant preferably isplaced behind the surface epithelium within the subconjunctival space.This is done by a surgical procedure that can be performed in anout-patient setting. A lid speculum is placed and a conjunctival radialincision is made through the conjunctiva over the area where the implantis to be placed. Wescott scissors are used to dissect posterior totenon's fascia and the implant is inserted. The conjunctiva isreapproximated using a running 10-0 vicryl suture. The eye has manybarriers that do not permit easy penetration of drugs. These include thesurface epithelium on the front of the eye and the blood/retinal barrierbehind the eye that both have tight junctions. Thus, in oneadministration strategy of the invention, the dual mode or single modematrix implant described herein is placed behind the surface epitheliumin the subconjunctival space. These subconjunctival implants aregenerally about 1-2 mm in diameter for small rodent (i.e., mouse andrat) eyes, 3-4 mm in diameter for rabbit and human eyes and 6-8 mm indiameter for equine eyes.

Additionally, when the subconjunctival matrix implant is placed near thelimbus (i.e., the area where the conjunctiva attaches anteriorly on theeye) to encourage the drug diffusion to enter the cornea, it ispreferable to fixate the matrix implant with one or two absorbablesutures (e.g., 10-0 absorbable vicryl sutures). This is done by makingholes with a 30 gauge needle in the peripheral portion of the implant,approximately 250-500 μm away from the peripheral edge of the implant.The holes are made 180 degrees from each other. This is done becausesubconjunctival matrix implants of this invention, when placed near thecornea, are at higher risk to extrude because of the action of the uppereye lid when blinking. When subconjunctival matrix implants of thisinvention are placed about 4 mm or more away from the limbus, thesutures are optional.

This matrix implant can deliver therapeutic levels of differentpharmaceuticals agents to the eye to treat a variety of diseases. Usinga rabbit model, drug released from the implant placed in the eyeproduces negligible levels of the drug in the blood. This significantlyreduces the chances of systemic drug side-effects.

In either case, whether the dual mode or single mode variants, thisembodiment of implant of this invention is well-tolerated and non-toxicto the patient or recipient, viz., a mammalian host-human or veterinary.In addition, this implant design of this invention is prepared by uniquemethodologies and selections of materials leading to and imparting theunique pharmacological performance properties present in the finisheddevices.

Among other eye therapies, the subconjunctival matrix implants of thepresent invention provide an effective treatment for cornealtransplantation procedures, where it is desirable to delivery an immunesystem modulator agent such as cyclosporine A non-systemically to theeye, in order to reduce rejection rates of corneal allografts. Thematrix implants containing 2ME2 can be attached to suture stubs andplaced in the vitreous humor for used in treatment of CNVM. 2ME2 is adrug manufactured by EntreMed, Inc., Rockville, Md., U.S.A., and iscurrently referred to as “Panzem”. The matrix implant also has potentialfor replacing the need for topical eye drops to treat certain eyediseases like glaucoma and uveitis and the implant has the potential totreat eye diseases in the back of the eye that are potentiallysight-threatening (e.g., retinal disease).

Also, for either the matrix implant, or the reservoir implant describedinfra, the drug released for the loading dose can be different than thedrug that is released for the long-term maintenance dose. For example,it may be advantageous to have a loading dose of corticosteroid from thedual mode implant for about a month postoperatively to reduce theinflammatory response resulting from surgery and have a continuousrelease of different drug to effect the disease that is being treated.

The drug pellets or tablets used for either the dual mode matriximplants, or the intraocular reservoir implants described elsewhereherein, are made by compressing a free-flowing powdered form of the drugin any suitable compression or molding machine, such as a pellet press.Pellet presses can be obtained, for example, from Parr InstrumentCompany, Moline, Ill. A force transducer can be used in ways one skilledin the art will appreciate to closely manage the compressive forceapplied. In the pellet press, the powdered form of the drug is enclosedwithin an open-mouthed cylindrical receptacle having a solid base and acontinuous inner wall defining the radial diameter and length(thickness) of the pellet to be formed. A ram applies a controlleduniform amount of pressure across the exposed surface of the powder fora given period of time sufficient to consolidate the powder into afree-standing solid pellet form.

Depending on the drug, binders and excipients for pellet-makingoptionally can be used. For example, magnesium stearate orhydroxypropylmethyl cellulose could be used. For example, for CsApellets (using 0.04% magnesium stearate as a binder) to be used incorneal transplantation treatments, a compressive pressure of about 110lb-force is used (for a round pellet, 3 mm diameter, 2 mm length) For2ME2 pellets for use in treatment of CNVM, a micronized preparation of2ME2 (size of drug particle is <5 micrometers) is used without binders,and a pressure of about 190 lb-force is used (for a round pellet, 2 mmdiameter, 3 mm length). The pressure consolidates the powder into anintegral, discrete solid pellet or tablet.

Reservoir Implants:

FIGS. 8A-I and 10A-D show methods for fabricating intraocular reservoirimplants according to this invention. The reservoir implants aresustained-release devices which deliver therapeutic agent to the eyeover a prolonged period of time. With some modifications describedherein, a loading dose or dual mode release capability also can be addedto the reservoir implants.

The reservoir implants generally include an implant reservoirsubassembly, a suture stub or other attachment means, and a means toadhere those two features together.

In general, the suture stub attachment means and adhering means includethe same respective materials described supra in connection with suturestubs optionally usable with intravitreal matrix implants, and referenceis made thereto.

As an alternative to the suture stub, a silk mesh fabric can be embeddedin one end of the reservoir type implant. This allows a suture to passthrough the one end and the suture will not scissor through the softsilicone since it is caught by the mesh. The suture then passes throughthe edges of the scleral wound and is tied down.

The discussion turns now to a method of making reservoir implantsubassemblies according to an embodiment of the reservoir implants ofthe invention.

Referring to FIG. 8A, a microcentrifuge tube 84 is provided of plasticconstruction, such as polyurethane, polypropylene or high densitypolyethylene construction, of suitable dimensions (e.g., ID of about 10mm and a length of about 40 mm), which can be obtained from PeninsulaLaboratories Inc., Belmont, Calif. As shown in FIG. 8A, themicrocentrifuge tubes have a tapered, conical-shaped bottom andcylindrical upper portion having an open end.

As seen in FIG. 8B, a curable (wet) silicone 86 fluid is poured into thelower section of the microcentrifuge tube 84 (e.g., about 10 mm depth).

The silicone used in making the reservoir implants is a medical gradesilicone, and generally is a polydimethylsiloxane (PDMS)-based compound.The silicone used is biologically (physiologically) inert and is welltolerated by body tissues. Suitable silicones for use in the practice ofthis embodiment include “MED-6810” silicone, MED1-4213, MED2-4213silicone, which can be obtained from NuSil, Carpinteria, Calif. Both ofthese silicones are two-part silicones including a metal curing system(e.g., Pt). The time and temperature needed to cure the silicone willdepend on the silicone used and the drug release profile desired. Thesesilicones, if left to cure at room temperature (e.g., 20-30° C.,) willrequire about 24 hours or more to cure. The cure rate will increase withincreasing cure temperatures. For instance, MED2-4213 silicone will curein about 30 minutes at about 100° C. As will be discussed in more detailbelow, the more quickly the silicone is cured, the less opportunity fortherapeutic agent to leach out into the surrounding silicone. Thus, themore rapid the curing, the less likely any burst or loading dose will beyielded by the device along with the slow steady state release action.

Referring to FIG. 8C, to provide a low adhesion, thin walled plastictube 82 shown, thin walled coiled polytetrafluoroethylene tubing, viz.,Teflon® tubing or the like releasable plastics, is heated at about 110°C. for about 30 seconds and then straightened, and thereafter cooled andset in the straightened orientation. The straightened low adhesionplastic was then cut into about 1.0 inch (2.54 cm) long tubes. TheTeflon® tubing is selected so as to have an outer diameter less than theinner diameter of the microcentrifuge tube, and the inner diameter ofthis low adhesion plastic tube must be larger than the radial diameterof a pellet to be encapsulated therein with silicone, as discussedbelow.

Referring still to FIG. 8C, soon after the wet silicone is introducedinto the microcentrifuge tube 84, one of the cut low adhesion plastictubes 82 is placed within the microcentrifuge tube. The low adhesionplastic tube 82 is spun vertically down a distance within the centrifugetube such that the lower end of the plastic tube 82 is submerged adistance “d” (e.g., about 3 mm) below the surface of the silicone 86already in the microcentrifuge tube 84 (distance “d” is best seen inFIG. 8E). The centrifuge device used can be a TOMY MTX-150 centrifuge,obtained from Peninsula Laboratories Inc., Belmont, Calif. The submergedportion 82 a of the plastic tube 82 is indicated in FIG. 8C. A portion86 a of the silicone 86 fills the lower 3 mm of the plastic tube 82, butanother portion 86 b fills space between the outside surface of the tube82 and the inner wall of the tube 84 in the lower section of the tube84.

Soon after introducing the tube 82 into microcentrifuge tube 84 in thismanner, the microcentrifuge tube 84 is centrifuged to degas the wetsilicone 86 and to radially center the tube 82 inside the outer tube 84.

At this juncture, the microcentrifuge tubes and contents are held atroom temperature (or optionally higher temperatures) until the silicone86 cures and solidifies, generally about 24-72 hours for roomtemperature cure. This hardens the portion of silicone 86 a locatedinside the lower end of the plastic tube 82, providing a solid siliconebase 86 a inside tube 82, and a hardened silicone 86 b outside tube 82which serves to retain it in an upright position.

Then, and as shown in FIG. 8D, a drug pellet 88 is introduced into theplastic tube 82 followed by adding additional uncured silicone fluid 86c into the tube 82. The microcentrifuge tube 84 is then centrifuged asneeded to degas the additional silicone 86 c and place, if necessary,the pellet 88 on the silicone base 86 a positioned at the bottom portion82 a of the plastic tube 82. The additional uncured silicone 86 c addedinside the plastic tube is sufficient to completely immerse the exposedsurfaces of the pellet 88 as it rests on the pre-hardened silicone base86 a. As needed, the drug pellet 88 can be manually or mechanicallycentered on the silicone base 86 a before curing silicone 86 c using aninsertable/retractable device or probe (such as a triple-0 Bowman probe)to move and center the pellet 88. The added silicone fluid 86 c is thencured inside the top portion 82 b of the plastic tube 82.

As shown in FIG. 8E, the microcentrifuge tube 84 is then removed bysharp dissection thereof with care taken not to disrupt the plastic tube82 or its contents. All of the silicone portions 86 a, 86 b and 86 cremain with the tube 82 at this juncture. Then as illustrated in FIG.8F, the silicone portion 86 b is manually separated from the exterior oftube 82 leaving tube 82 containing silicone portion 86 a and 86 csandwiched over the pellet 88. Next, as shown in FIG. 8G, plastic tube82 is removed by sharp dissection in which the plastic tube 82 has atransverse cut made at the lower end thereof with a blade, and the tube82 is then split away from the internal silicone/pellet complexsubassembly 89. FIG. 8H shows the internal silicone/pellet complexsubassembly 89 after removal of the low adhesion plastic tube 82. Asshown in FIG. 81, the top and bottom ends of the reservoir implantsubassembly are trimmed closer to the top and bottom ends of the drugpellet 88 to provide a finished reservoir implant subassembly 89. FIGS.9A-C show various enlarged views of the resulting reservoir implantsubassembly 89 comprised of the silicone-encased drug pellet.

Referring now to FIG. 7, a reservoir implant subassembly 71 made in thismanner is attached to a suture stub 73, such as one constructed ofprocessed Airvol 650 as described above, using a silicone adhesive 75,such as Nusil MED1-4213. The suture stub can be used to fasten theimplant reservoir in the eye such that it cannot drift or move about.

Reservoir implant subassemblies 121 made in this manner with variousdrugs in the reservoir, e.g., leflunomide (lef) or 2-methoxyestradiol(2ME2), have been adhered to Airvol 350 suture stubs using siliconadhesive (see FIG. 12A) in order to examine the release properties. Foreach drug, 3 different diameters (inner) of Teflon® tubing were used tomake implants with polymer thicknesses (i.e., 0.20, 0.36, and 0.70 mm),as described in Example 8 infra, to provide a thin-walled “mold” for theradial dimensions of the silicone encasement to be formed around thepellet. As seen in FIGS. 13 and 14, the reservoir implants had lowerrelease rates with increasing polymer thickness, radial and/ortop/bottom, surrounding the drug pellet.

By varying the sizes of pellets and Teflon® tubing it is possible tocreate many thicknesses of polymer surrounding the implant, as shown inTable A below. Table A reports such polymer thicknesses for variouspellet sizes and various tube gauges (i.e., 8, 9, and 10 gauge). Atypical releasable tubing used is PTFE (Texloc, LTD. Fort Worth, Tex.).The release rate of a reservoir implant according to this invention isstrongly dependent upon the thickness of the polymer coating. For acylindrical reservoir implant device containing a cylindrical drugpellet radially centered within the silicone cladding, this relationshipis described by the following formula:

dM _(t) /dt=2πhDKC _(s)/(ln r ₀ /r ₁)

where dM_(t)/d_(t) is the release rate, r₀ is the outside radius of theimplant, r₁ is the radius of the drug pellet, h is the height of thecylinder, D is the diffusion coefficient of the drug through thepolymer, K is the distribution coefficient and C_(s) is the solubilityof the drug in the fluid.

TABLE A Thickness of Polymer Coating (mm) Pellet Tubing Diam. Sizes(gauge) (mm) 8 9 10 0.5 1.45 1.26 1.11 1.0 1.20 1.01 0.86 1.5 0.95 0.760.61 2.0 0.70 0.51 0.36 2.5 0.45 0.26 0.11 3.0 0.20 0.01 0

This method for preparing the intraocular reservoir implant of thisinvention provides an implant having a controlled radial thickness ofdegassed silicone cladding around the drug pellet with no significantvariability in the cladding thickness from one coated pellet to thenext. Also, rigorous post-production quality control inspections(including measuring individual implant release rates before in vivouse) of the implant products are not necessary, which reduces thechances for contamination of the device from additional handling as wellas the cost of making the devices. Drug pellets of the medicament can bemade using a Parr pellet press, as described earlier.

Modifications available to adjust the drug administration of thereservoir implants include:

an intravitreal reservoir dual mode implant further includingtherapeutic agent 127 dispersed in the silicone 121′ surrounding thedrug pellet 121″ of the reservoir implant subassembly 121 (FIG. 12B);

an intravitreal reservoir dual mode implant including therapeutic agent127 dispersed in a silicone adhesive 125 used to attach the reservoirimplant subassembly 121 to the suture stub 123 (FIG. 12C);

an intravitreal reservoir dual mode implant including therapeutic agentprovided in an inlay 129 attached to a silicone adhesive 125 used toattach the reservoir implant subassembly 121 to the suture stub 123(FIG. 12D); and

a double-barreled intravitreal reservoir implant configuration includingtwo reservoir implant subassemblies 121A and 121B attached to a commonsuture stub 123 (FIG. 12E). This configuration effectively increases thesurface area of drug release from the central pellet to correspondinglyincrease the maintenance release rates.

The drug delivery behavior of the intraocular reservoir implants (121,123), as mounted on a suture stub as described above, is schematicallyshown in FIGS. 11A (initial loading dose 103) and 11B (long termsustained or maintenance dose 105), for an implant placed in an eye 101as shown in FIG. 11C.

As another dual mode embodiment of the reservoir implant, and as shownin FIGS. 10A-D, a circular wafer shaped pellet 107 of therapeutic agent,which has a tablet shape by having a larger radial diameter thanthickness, is fixed at its lower surface to a suture stub 109 withsilicone adhesive (not shown), such as the above-mentioned NusilMED1-4213 silicone adhesive. The dimensions of the wafer-shaped pelletor tablet could be, for example, 1-2 mm in height and 3 mm in radialdiameter. A temperature-curable silicone adhesive, such as the same typeabove (e.g., NuSil MED1-4213 silicone adhesive), is then used to form abead or ribbon of wet silicone 111 around the periphery of the tablet107 (i.e., coating the side edge surfaces of the tablet and contactingthe adjoining surface of the suture stub). Then, the cure of thesilicone bead coating is slowed or delayed preferably for about 18 to 30hours, more preferably approximately 24 hours, by keeping the coatedassembly at room temperature (e.g., 20-30° C.). The upper flat surfaceof the tablet is covered with thin silicone coating 113, such asMED1-4123 or Nusil MED-6810 (a two-part silicone) that is cured with(radiant) heat before or after the “delay in cure” procedure isconducted on the peripheral silicone bead coating. During the interimdelay in cure period when the silicone adhesive is gradually and slowlycuring, some, but not all, of the therapeutic agent diffuses into thesurrounding unfully cured bead of silicone polymer, which creates asignificant burst or loading dose when the implant is installed,followed by slow, lower dosage sustained release of the therapeuticagent. This effect is shown by FIG. 10E, which relates to in vitro testsperformed on this class of reservoir implants where the tested implantsincluded 2ME2 tablets of about 1.5 mm height and 3 mm in diameter, thebottom and peripheral bead silicone adhesive was NuSil MED1-4213silicone adhesive, and the top surface silicone coating was NusilMED-6810 applied and cured after the “delay in cure” procedure.

Certain silicones, such as MED1-4123, that contact the drug pellet in awet phase for a long period of time, yield more substantial loadingdosages. By using this drug leaching to advantage, and using siliconesthat can quick cure (MED2-4123 or the 6810), it is possible to controlthe degree of drug loading by curing at differential times.

The reservoir implants of this invention can be used to treat a numberof eye diseases and indications including, for example, age-relatedmacular degeneration, glaucoma, diabetic retinopathy, uveitis,retinopathy of prematurity in newborns, choroidal melanoma, chorodialmetastasis, and retinal capillary hemangioma. For these indications, asuitable therapeutic agent includes, for example, 2-methoxyestradiol.For example, the reservoir implant provides for a sustained release ofdrugs, such as 2-methoxyestradiol for the treatment of undesirableangiogenesis involved in the degeneration of the macula.

The loading dose from the reservoir implant can be estimated when thetarget drug concentrations in the vitreous and drug clearance from theeye is known. Assuming a one-compartment model with no partitioning, thesteady-state concentration (Css) is the release rate timesbioavailability (F) divided by the clearance (CL). Benet, L., et al.,Pharmokinetics In: Goodman and Gilman's: The Pharmacological Basis ofTherapeutics. New York: McGraw-Hill; 1996: 3-27. This relationship isexpressed by the following formula:

(Css)=steady-state implant release rate×F/CL (1).

The fractional bioavailability of the dose (F) can be assumed to be 1for intravitreal implants and <1 for subconjunctival implants (sincesome drug is lost en route to the vitreous cavity through theconjunctival, episcleral, and choroidal vasculature). Classicpharmacokinetics teach that steady state concentrations can be obtainedafter approximately four half-times. For example, the CL of anantimetabolite from the vitreous cavity, when scaled to humans, is 0.38ml/hr and the half life is 10.4 hours. Velez, G., et al., IntravitrealChemotherapy for Primary Intraocular Lymphoma. Arch Ophthalmol (inpress). 2001.

If the target concentration in the vitreous is 1 μg/ml, a release rateof 0.38 μg/hr will be required to achieve Css in the vitreous afterapproximately 4 half times or 41.6 hours. For comparison, if the drug isbeing released by a subconjunctival matrix implant according to thisinvention, with a bioavailability of 0.5, the release rate from theimplant would need to be doubled (i.e., 0.76 μg/hr).

For conditions, such as CNVM associated with AMD, long delays (i.e.,41.6 hours) are not desirable. Loading doses from the implant canshorten the length of time required to reach Css. For example, using theequation:

V _(d)*(dC/dt)=I(t)−CL*C(t)

where V_(d) is the volume of distribution, C is the concentration ofdistribution, dC/dt is the rate of change of concentration in thevitreous, I(t) is the release rate from the implant. The notation withparentheses (t) indicates that the rate may change with time, forexample, a rapid release on and then settling to a lower rate for aprolonged period of time.

A doubling of the release rate of an intravitreal implant for a periodequal to the half-life of the drug allows Css to be reached in onehalf-time (10.4 hours) instead of four half-lives (41.6 hr). To furtherincrease the speed at which the Css is reached, for example, in 2 hrs(20% of a half-life) after the implant is placed, the drug release rateshould be approximately 8 times higher during that period.

The reservoir implants have been designed to release a loading dose ofdrug within the first few hours after implant placement. For example,using the ‘cure time delay’ technique, periods of delay in the curingthe silicone around the drug pellet can change the drug burst from theimplant; however, the reservoir implants continue to release a steadystate concentration after the loading dose.

The therapeutic agents and drugs that can be delivered by the variousmatrix and reservoir implants of this invention include, for example:

antibiotic agents such as fumagillin analogs, minocycline,fluoroquinolone, cephalosporin antibiotics, herbimycon A, tetracycline,chlortetracycline, bacitracin, neomycin, polymyxin, gramicidin,oxytetracycline, chloramphenicol, gentamicin and erythromycin;

antibacterial agents such as sulfonamides, sulfacetamide,sulfamethizole, sulfoxazole, nitrofurazone, and sodium propionate;

antiviral agents such as idoxuridine, famvir, trisodiumphosphonoformate, trifluorothymidine, acyclovir, ganciclovir, DDI andAZT, protease and integrase inhibitors;

anti-glaucoma agents such as beta blockers (timolol, betaxolol,atenolol), prostaglandin analogues, hypotensive lipids, and carbonicanhydrase inhibitors;

antiallergenic agents such as antazoline, methapyriline,chlorpheniramine, pyrilamine and prophenpyridamine;

antiinflammatory agents such as hydrocortisone, leflunomide,dexamethasone phosphate, fluocinolone acetonide, medrysone,methylprednisolone, prednisolone phosphate, prednisolone acetate,fluoromethalone, betamethasone, triamcinolone acetonide, adrenalcorticalsteroids and their synthetic analogues, and 6-mannose phosphate;

antifungal agents such as fluconazole, amphotericin B, liposomalamphotericin B, voriconazole, imidazole-based antifungals, triazoleantifungals, echinocandin-like lipopeptide antibiotics, lipidformulations of antifungals;

polycations and polyanions such as suramine and protamine;

decongestants such as phenylephrine, naphazoline, and tetrahydrazoline;

anti-angiogenesis compounds including those that can be potentialanti-choroidal neovascularization agents such as 2-methoxyestradiol andits analogues (e.g., 2-propynl-estradiol, 2-propenyl-estradiol,2-ethoxy-6-oxime-estradiol, 2-hydroxyestrone, 4-methoxyestradiol), VEGFantagonists such as VEGF antibodies and VEGF antisense, angiostaticsteroids (e.g., anecortave acetate and its analogues,17-ethynylestradiol, norethynodrel, medroxyprogesterone, mestranol,androgens with angiostatic activity such as ethisterone);

adrenocortical steroids and their synthetic analogues includingfluocinolone acetonide and triamcinolone acetonide and all angiostaticsteroids;

immunological response modifying agents such as cyclosporine A, Prograf(tacrolimus), macrolide immunosuppressants, mycophenolate mofetil,rapamycin, and muramyl dipeptide, and vaccines;

anti-cancer agents such as 5-fluoroucil, platinum coordination complexessuch as cisplatin and carboplatin, adriamycin, antimetabolites such asmethotrexate, anthracycline antibiotics, antimitotic drugs such aspaclitaxel and docetaxel, epipdophylltoxins such as etoposide,nitrosoureas including carmustine, alkylating agents includingcyclophosphamide; arsenic trioxide; anastrozole; tamoxifen citrate;triptorelin pamoate; gemtuzumab ozogamicin; irinotecan hydrochloride;leuprolide acetate; bexarotene; exemestrane; epirubicin hydrochloride;ondansetron; temozolomide; topoteanhydrochloride; tamoxifen citrate;irinotecan hydrochlorise; trastuzumab; valrubicin; gemcitabine HCL;goserelin acetate; capecitabine; aldesleukin; rituximab; oprelvekin;interferon alfa-2a; letrozole; toremifene citrate; mitoxantronehydrochloride; irinotecan HCL; topotecan HCL; etoposide phosphate;gemcitabine HCL; and amifostine;

antisense agents;

antimycotic agents;

miotic and anticholinesterase agents such as pilocarpine, eserinesalicylate, carbachol, diisopropyl fluorophosphate, phospholine iodine,and demecarium bromide;

mydriatic agents such as atropine sulfate, cyclopentane, homatropine,scopolamine, tropicamide, eucatropine, and hydroxyamphetamine;

differentiation modulator agents;

sympathomimetic agents such as epinephrine;

anesthetic agents such as lidocaine and benzodiazepam;

vasoconstrictive agents;

vasodilatory agents;

polypeptides and protein agents such as angiostatin, endostatin, matrixmetalloproteinase inhibitors, platelet factor 4, interferon-gamma,insulin, growth hormones, insulin related growth factor, heat shockproteins, humanized anti-IL-2 receptor mAb (Daclizumab), etanercept,mono and polyclonal antibodies, cytokines, antibody to cytokines;

neuroprotective agents such as calcium channel antagonists includingnimodipine and diltiazem, neuroimmunophilin ligands, neurotropins,memantine and other NMDA antagonists, acetylcholinesterase inhibitors,estradiol and ananlogues, vitamin B12 analogues, alpha-tocopherol, NOSinhibitors, antioxidants (e.g. glutathione, superoxide dismutase),metals like cobalt and copper, neurotrophic receptors (Akt kinase),growth factors, nicotinamide (vitamin B3), alpha-tocopherol (vitamin E),succinic acid, dihydroxylipoic, acid, fusidic acid;

cell transport/mobility impending agents such as colchicine,vincristine, cytochalasin B;

carbonic anhydrase inhibitor agents;

integrin antagonists; and

lubricating agents, singly or in combinations thereof.

This listing of therapeutic agents is illustrative, and not exhaustive.Other drugs that could be delivered by the ocular implant include, forexample, thalidomide.

Reference can be made to Remington's Pharmaceutical Sciences, MackPublishing Press, Easton, Pa., U.S.A., to identify other possibletherapeutic agents for the eye. Any pharmaceutically acceptable form ofthe agents can be used, such as the free base form or a pharmaceuticallyacceptable salt or ester thereof.

Among other things, this invention includes dual mode implants andrelated treatments effective to saturate all compartments of the eye vialarge initial loading dose release and then provide a sustainedmaintenance dosage to the target area of the eye thereafter over anextended period of time. Because the ocular tissues are not homogenous,and also because many drugs to be used in the eye are lipophilic,ideally a large loading dose should be initially delivered by an ocularimplant, and once all the tissues of the eye are saturated, then uniformlower yet maintenance levels of the drug need to be released over anextended period of time by the implant which can more easily gravitateto the target areas of the eye for treatment.

The Examples that follow are intended to illustrate, and not to limit,the invention. All percentages used herein are by weight, unlessotherwise indicated.

EXAMPLE 1

This example illustrates the preparation of a matrix implant of theinvention useful for subconjunctival implants.

4.5 g of superhydrolyzed polyvinyl alcohol (Airvol 125, Air Products andChemicals, Inc., Allentown, Pa., U.S.A.) was added to 30 ml of molecularbiology grade water in an assay tube that was then tightly closed. Thetightly closed assay tube was placed in a beaker of boiling water untilthe density becomes uniform (generally about 3-7 hrs). Since the assaytube was tightly closed, the contents could not evaporate. Water wasperiodically replaced in the beaker to keep the water height near theheight of water in the assay tube. The assay tube was centrifuged for 1minute at 1000-4000 rpm to degass the mixture. This formed a 15 wt %solution of superhydrolyzed polyvinyl alcohol.

Separate premixtures were prepared using each of cyclosporine A and 2ME2as the therapeutic agent. Each therapeutic agent was separately premixedin a solution of hydroxypropyl methylcellulose (HPMC), obtained asMETHOCEL E4M from Dow Chemical, Midland, Mich., in amount of 0.05 wt %about (on a dry basis; drug plus HPMC). In this regard, 500 mg of drugwas combined and mixed with 2.25 g HPMC. For instance, the cyclosporineA (or 2ME2) powder was placed in microbiology grade water (i.e.,endotoxin free water) with the HPMC and mixed with a stir bar, no heat,for up to 24 hours. The superhydrolyzed PVA solution was then combinedwith the HPMC/drug mixture with a spatula. For more highly viscoussuspensions, a blender may be desirable. As such a blender, aMiniContainer is adapted to the blender to hold small volumes, where theblender is a Laboratory Blender (Model 51BL30), operated at speeds of18,000 rpm (low) or 22,000 rpm (high) as needed. The Mini Container(MMGC1) was stainless steel and held 12-37 ml, and was obtained fromWaring Factory Service Center, Torrington, Conn. To add the materials toa blender, a bottom of the assay tube containing the PVA/METHOCEL/drugmixture is cut with a razor blade and the contents poured into theblender. In one method, the mixture is blended at high speed (22K RPM)for up to 5 minutes, and the blended contents are then poured into a 50ml assay tube and centrifuged for 2 minutes at 1000-4000 rpm to degasit.

The resulting highly viscous superhydrolyzed PVA/HPMC/drug mixtures wereinjected with a large volume syringe between 2 glass plates (6×6inches). Spacers (1-5 mm thick) were placed between the glass plates.This allowed a measured thickness of mixture to be applied to the glassplate. This complex was the placed at 0° C. for up to 30 minutes.Chilling the glass plates sufficient that the top glass plate could beremoved without impairing the matrix layer. The top plate was removed inthis manner. The mixture was then left attached to the other bottomglass plate and allowed to air dry at room temperature for approximately15 hours.

To make dual mode subconjunctival matrix implants, compressed drugpellets were formed to the desired dimensions using a Parr pellet press(Parr Instrument Co., Moline, Ill., USA). Also, before theabove-mentioned chilling step performed on the glass plates, the topglass plate was temporarily moved sufficient to permit access to thesurface of the wet coating so that the pellet could be lightly pushed ortapped on its upper surface, such as using a Bowman's probe, into thewet coating layer deep enough that the pellet is completely immersed andembedded within the coating layer. At least one mm coating is providedon each side of the pellet in this example, although smaller uniformthicknesses could be used. The top glass plate was replaced again overthe surface of the coating layer (now containing the embedded pellet),and the glass plates were chilled as described above. Then, the topglass plate was removed.

After the slab had dried for about 15 hours, trephines (skin BiopsyPunches) (Acuderm Inc., Ft. Lauderdale, Fla.) of varying diameters wereused to make the implants. A trephine of dimensions of at least 1 mmgreater than pellet diameter was used to punch out pellets. The punchedpieces were permitted to sit for 48 additional hours and then irradiatedwith a low dosage of (e.g., about 3 megarads of gamma radiation) forsterilization purposes only, such that significant levels ofcrosslinking does not occur.

EXAMPLE 2

This example illustrates the preparation of another matrix implant ofthe invention, which is useful as an intravitreal implant.Alternatively, this matrix implant can be used for an inlay used incombination with reservoir implants of the invention described elsewhereherein.

Preparation of 50% superhydrolyzed PVA, 6% 2ME2, 0.05% HPMC matriximplant:

The polymer drug mixture was prepared in a 3 cc syringe (the tip sealedwith a Luer lok and a HPLC septum). The plunger was removed. A drugemulsion was prepared by adding 63.8 mg 2ME2 and 0.5 mg hydroxypropylmethylcellulose (E4M, Dow Chemical) to 2 ml molecular grade biologicalwater. The emulsion was mixed with a magnetic stirrer over night, andthen it was added to 1 g superhydrolyzed PVA (Airvol 125; Air Productsand Chemicals, Inc., Allentown, Pa., U.S.A.) in the syringe. The mixturewas stirred until uniform and then placed into a water bath at about100° C. for 60 minutes. The sample with the syringe was then spun downfor 2 minutes at 2000 rpm to dislodge air bubbles. It was then returnedto the 100° C. water bath for 15 minutes to make it pliable. Theoriginal plunger was inserted into the syringe and a small hole was madejust above the drug/polymer sample to prevent reintroduction of air intothe sample. The tip of the syringe was then cut off and the sampleejected onto a glass plate. Using spacers, another plate is used tosandwich the sample the resulting sandwich is then cooled at 5° C. for30 minutes. The glass plates were separated and the sample dried underambient conditions for 24 hours and then under vacuum for 48 hours. Theimplants were then cut to size using a razor blade. For dual modeimplants made from this slab, 0.5 mm drug pellets (generally 0.3 to 1.0mm long and about 100 μg to 500 μg) were inserted into the space betweenthe glass plates before refrigerating. This was done by placing thepellets in the coating layer at the edges thereof where the two glassplates come together and the coating layer is exposed. Once the PVA slabwas desiccated, the dual action implants were cut in the desired shape(e.g., circular) leaving the desired amount of drug loaded PVA aroundthe drug pellet.

EXAMPLE 3

A 1×1×2 mm matrix implant was prepared using poly(ethylene vinyl)acetate (EVA) in place of superhydrolyzed PVA in the subconjunctivalimplant.

Preparation of 30% EVA, 6% 2ME₂, 0.05% HPMC matrix implants:

The polymer drug mixture was prepared in a 3 cc syringe (the tip sealedwith a Luer lok and a HPLC septum). The plunger is removed. A drugemulsion is prepared by adding 38.3 mg 2ME2 and 0.3 mg HPMC (E4M, DowChemical) to 2 ml methylene chloride. The emulsion is mixed over nightwith a magnetic stirrer and then transferred to a 10 ml vial containing0.6 g EVA (Elvax 40W, Dupont). The mixture was stirred with a magneticstirrer until it becomes too viscous. The magnetic stirrer was thenremoved and the mixture was left overnight. The sample was centrifugedas needed to degass the specimen. The specimen was poured onto a glassplate and permitted to dry for 48 hours under vacuum. The implants werethen cut to size using a razor blade, e.g., multiple 1×1×2 mm slabs orwafers. For dual mode implants, 0.5 mm drug pellets that are generally0.3 to 1.0 mm long and about 200 μg) are inserted until fully embeddedin a centered manner in the wet EVA/drug mixture after it was poured outon the glass. Once the slab was desiccated, the dual action implantswere cut leaving a desired amount of drug loaded EVA around the drugpellet.

EXAMPLE 4

Matrix implants of this invention were used in a study to document thein vitro release rates of single and dual mode CsA implants to evaluatetheir usefulness for the treatment of eye diseases, such as high riskcorneal transplantation. In addition, to evaluate the feasibility ofusing these implants in humans, rabbit studies were performed to assaythe ocular drug levels following the insertion of these implants in thesubconjunctival space. The ocular toxicity of these implants wereevaluated by electroretinography (a test of retinal function) andhistopathology.

Methods:

In Vitro Studies

Two matrix implant designs were studied, i.e. single and dual mode CsAimplants, designated Matrix Implant (1) and (2), respectively.

A Matrix Implant (1) was made generally according to the protocoldescribed in Example 1 except without adding the drug pellet. That is, asuperhydrolyzed PVA solution made using 4.5 grams of Airvol 125 (AirProducts and Chemicals, Inc., Allentown, Pa., U.S.A.), in solution, wascombined with 5 ml of an emulsion of CsA. The CsA emulsion wasseparately previously prepared as a premixture of 0.5 g powderedCsA,(USP-23, Xenos Bioresources, Inc., Santa Barbara, Calif.) and 0.0023g HPMC (METHOCEL E4M, obtained from Dow Chemical, Midland, Mich.) in 5ml of microbiology grade water. The combined PVA and CsA/HPMC solutionsgave a 10% CsA concentration by weight. The PVA/HPMC/CsA aqueous mixturewas mixed at 70° C. for 30 minutes. The PVA/HPMC/drug suspension wasplaced between glass plates. Upon drying, a uniform film of 0.5-mmthickness was produced in the manner described in Example 1. A 3-mmtrephine was used to cut circular implant discs from the resulting film.

Matrix Implant (2) was made using the same procedure as above except a1.5 mg compressed CsA drug pellet of a thickness of 2.0 mm was embeddedwithin the center of the circular disc. To embed the pellet, the pelletwas embedded within the coating layer in the manner described in Example1.

In-vitro release rates were determined by placing the implants in PBS(pH 7.4) at 37° C. and assaying drug levels over time by HPLC.

In Vivo Studies:

Ocular Drug Levels:

Eight New Zealand White rabbits (16 eyes) of either sex weighing 2-3 kgwere used in this study and the procedures adhered to the guidelinesfrom the Association for Research in Vision and Ophthalmology for animaluse in research. Animals were anesthetized with ketamine hydrochloride(Fort Dodge, Inc., Fort Dodge, Ind.) (35 mg/kg) IM, xylazine (PhoenixScientific, Inc., St. Joseph, Mo.) (5 mg/kg) IM, and proparacaine 1%ophthalmic drops (Allergan America, Hormigueros, Puerto Rico) were usedtopically on the eye. A lid speculum was placed and a 4 mm conjunctivalradial incision was made through the conjunctiva 1 mm from the limbusand 3 mm nasal to the superior rectus muscle. Wescott scissors were usedto dissect posterior to Tenon's fascia and the implant was inserted withits anterior edge 3 mm from the limbus and secured to the episclerausing a single interrupted 10-0 suture. The conjunctiva wasreapproximated using a running 10-0 suture. In vivo studies wereperformed using the dual mode CsA implant because of its potential torelease CsA for an extended period of time to treat eye diseases. Theright eye of each rabbit received a dual mode CsA implant.Postoperatively, bacitracin-neomycin-polymyxin ophthalmic ointment(Pharmaderm, Melville, N.Y.) was placed in both eyes twice daily(2×/day) for 3 days. The animals were examined regularly and euthanizedwith a pentobarbital overdose (Beuthanasia-D Special, Scheming-PloughAnimal Health Corp., Kemilworth, N.J.) 2 months post-implantation. Botheyes were enucleated. Eyes from 5 rabbits had a 5×5 mm section ofconjunctiva both over the implant and 180° away isolated for drugextraction. The implants were firmly attached to the episclera and theywere gently peeled away from the underlying tissues. The globes wereimmediately frozen at −70° C. for later dissection and drug extraction.The time from enucleation to freezing was rapid (<10 seconds) whichlimited postmortem drug redistribution. The eyes were dissected whilefrozen and a 5'5 mm section of full thickness sclera beneath the implantand 180° away was isolated. Other tissues (cornea, aqueous humor, lens,and vitreous humor) were isolated for separate drug analysis. The CsAwas extracted from the tissues by the addition of an equivalent weightof HPLC grade Acetonitrile (Burdick & Jackson, Inc., Muskegon, Mich.),sonicated for 45-90 seconds with a model GEX 600 Ultrasonic processor(Thomas Scientific, Swedesboro, N.J.) and incubated for 24 hours at roomtemperature. The samples were spun down in a TOMY MTX-150 centrifuge(Peninsula Laboratories Inc., Belmont, Calif.) for 30 minutes at 10,000rpm and the supernatants were submitted for HPLC analysis. The CsAconcentrations in the tissues were expressed as μg/g wet weight (mean)for the solid tissues and μg/ml (mean) for the aqueous and vitreoushumor.

Eyes from 3 rabbits were placed in formalin 10% (Biochemical Science,Inc., Swedesboro, N.J.) for at least 7 days, embedded in paraffin, andsectioned for histopathology.

Ocular Toxicity Testing (Electroretinography):

The rabbits were anesthetized using the same procedures detailed aboveand the pupils were dilated with 1 drop of phenylephrine hydrochloride2.5% (Akorn, Inc., Decatur, Ill.) and tropicamide 1% (Alcon, Inc.,Humacao, Puerto Rico). ERGs were recorded from each eye separately after30 minutes of dark adaptation. A monopolar contact lens electrode(ERG-jet, La Chaux des Fonds, Switzerland) was placed on the cornea andserved as a positive electrode. Subdermal needle electrodes inserted inthe forehead area and near the outer canthus served as the ground andnegative electrodes, respectively. ERGs were elicited by flash stimulidelivered with a Grass PS22 photostimulator (Grass Instruments, Quincy,Mass.) at 0.33 Hz. Responses were amplified, filtered and averaged witha Nicolet Spirit signal averager (Nicolet Instruments Corp., Madison,Wis.). Averages of 20 responses were measured to obtain amplitude andimplicit time values of a-waves and b-waves. Recordings were performedat baseline, and 1 and 2 months post-implantation. A permutation test ofmean amplitude differences and analysis of variance of the logarithmictransform of amplitudes were performed to determine statisticallysignificant changes between readings.

Results:

The single mode Matrix Implant (1) produced an initial loading dose ofCsA (12.54+/−1.47 μg/day) with a logarithmic decline to <0.5 μg/day byday 31 (see FIG. 4A), while Matrix Implant (2) produced an initialloading dose of CsA (39.9+/−10 μg/day) with a logarithmic decline inrelease rate to 7.67+/±1.79 μg/day by day 38 (FIG. 4B). Daily releaserates reached a steady state release of 6 μg/day after day 40 and therelease rates were predicted to be stable for 18 months.

CsA Levels in Tissues:

Five rabbits had the eye with the dual mode CsA implant processed todetermine CsA concentrations. The distribution of the CsA in the eye isshown in FIG. 13. Corneal levels of 2.25 μg/g (mean) were present whichare potentially therapeutic for the treatment of graft rejection.Unexpectedly, an unusually high concentration of CsA was present in thevitreous (21.78 μg/ml (mean)) which can potentially be therapeutic forthe treatment of posterior segment inflammatory diseases.

Ocular Toxicity Testing:

Electroretinography showed no signs of retinal toxicity from the CsAimplants. Histopathologic examination of eyes from 3 rabbits with thedual mode implant was performed by light microscopy. The conjunctivaoverlying the implant and the sclera beneath was intact. All ocularstructures appeared intact with a mild chronic inflammatory infiltratepresent in the substantia propia of the conjunctiva overlying theimplants in all eyes. The peripheral retina anterior to the equatorshowed some vacuolated spaces predominantly in the photoreceptor layerin both eyes but the photoreceptor layer in the posterior segment of theeye along the medullary rays was normal.

Conclusions:

These results demonstrated that single mode Matrix Implant (1)subconjunctival implant can deliver potentially therapeutic levels ofCsA to the eye for approximately a month. The dual mode Matrix Implant(2) subconjunctival implant could deliver an initial loading dose of CsAlasting 1 month followed by a steady state sustained-release delivery ofCsA as a maintenance dose for at least 1 year. The implants weredetermined to be reasonably safe by histopathological examination and byelectroretinography.

The implant was initially designed to release CsA into the cornea forprevention of graft rejection in patients with high risk cornealallografts. To this end, the implants delivered potentially therapeuticlevels of CsA to the cornea. This study revealed an unexpected findingthat the dual mode implant representing an embodiment of this inventiondelivered high levels of CsA in the vitreous cavity. Since the vitreouscavity is in direct contact with the retina and the other importanttissues of the eye, the subconjunctival implant (which is installedoutside the eye) has the potential to treat many intraocular diseases.

EXAMPLE 5

A study was performed to investigate the use of 2-methoxyestradiol inintravitreal matrix implants of this invention in a rat model ofchoroidal neovascularization (CNV).

Methods:

Implant Design:

2ME2 dry powder was premixed in a solution containing 0.05% HPMC thenmixed with a 50% polyvinyl alcohol (PVA) solution to produce a 6% (bydry weight) 2ME2 matrix suspension (see example 2 for details). Thesuspension was poured onto a glass plate producing a thin film, dried atroom temperature, and cut into 1.0×1.0×2.0 mm sections, each sectionrepresenting one implant. Sham implants (PVA without drug) were made ina similar fashion. In-vitro release rates were determined by placing theimplants in PBS and assaying drug concentrations over time with HPLC.

CNV Model:

Fifteen Brown-Norway rats were used. An E1-deleted adenoviral vectorencoding human VEGF165 was injected (2.5×10⁴ pfu/μL) into the subretinalspace nasal to the disc of one eye using a 32 gauge needle. In the sameeye, a 2 mm full-thickness scleral incision was made temporally and 2ME2implants were placed in the vitreous cavity of 9 eyes and sham implantsplaced in 8 eyes. The sclerotomy was closed using a 10-0 nylon suture.Five rats (3 with 2ME2 and 2 with sham implants) were euthanized at 1week. Five rats (2 with 2ME2 and 3 with sham implants) were euthanizedat 2 weeks. Five rats (2 with 2ME2 and 3 with sham implants) wereeuthanized at 3 weeks. The implant eyes were enucleated, fixed informalin and embedded in methacrylate-JB4. The eyes were sectioned inthe area of injection (75 total, 3 μm sections), counterstained with H&Eand examined with a light microscope for choroidal neovascularization.The maximal axial length of the CNV was recorded in micrometers.

Results:

In vitro Release Rates of 3 Implants:

The mean in-vitro release rates (graph below) followed first-orderkinetics, typical of matrix implants. The implants released 2ME2>1μg/day over 30 days, as shown in FIG. 15.

CNV Model:

CNV was present in 1/9 eyes with the 2ME2 implant: the axial length ofthe one membrane=46.5 μm. A proliferation of RPE cells in a bi ortri-layer was present in all 3 eyes at 1 week. CNV was present in 5/8eyes with the sham implant: mean axial length=347.4 μm.

Results:

These results demonstrated that the sustained-release 2ME2 microimplantsrepresenting this invention can successfully suppress choroidalneovascularization in a rat model.

EXAMPLE 6

The dual mode reservoir implants were made and tested in vitro forrelease rate behavior.

Methods:

Three designs were constructed using 2ME2 compressed in a customizedParr pellet press to 190 lb force.

Design Summary:

Design A: A 2ME2 pellet (3 mm, mean weight 23.0 mg) was coated with 0.20mm silicone (using 8 gauge, 3.28 mm internal diameter PTFE (Teflon)tubing from Texloc, LTD. Fort Worth, Tex.);

Design B: A 2ME2 pellet (2 mm, mean weight 10.5 mg) was coated with 0.36mm silicone (using 10 gauge, 2.59 mm internal diameter PTFE tubing);

Design C: A 2ME2 pellet (2 mm, mean weight 10.5 mg) was coated with 0.70mm silicone (using 8 gauge, 3.28 mm internal diameter PTFE tubing)

A microcentrifuge having an ID of about 10 mm and a length of about 40mm, was obtained from Peninsula Laboratories Inc., Belmont, Calif.U.S.A. The microcentrifuge tube was filled with MED-6810 about 10 mm indepth.

To make uniform silicone coatings of 0.20 mm, 0.36 mm and 0.70 mm aroundthe drug pellets, thin walled plastic tube (PTFE teflon tubing fromTexloc, LTD. Fort Worth, Tex.) was used. The PTFE tubing was heated at110 degrees celsius for 30 seconds and then straightened, cut into 1.0inch (2.54 cm) long tubes, and thereafter cooled and set in thestraightened orientation in the microcentrifuge tube. Themicrocentrifuge tube was centrifuged to degas the wet silicone and toradially center the PTFE tube. The silicone was then cured with heat(100° C. for 30 minutes). The pellet sizes and PTFE tubing diametersused for the 3 designs are detailed supra.

The 2ME2 drug pellet was introduced into the PTFE tubing followed byadding additional fresh MED-6810 silicone sufficient to immerse thepellet. The microcentrifuge tube was then centrifuged as needed to degasthe additional silicone. As needed, the drug pellet was manually ormechanically centered on the silicone base before curing the addedsilicone using a Bowman probe. Drug loading was performed using the‘delay in cure’ technique. That is, the pellets were left in the wetsilicone for a total of 1 hour and then cured for 1 hour at 100° C.

In vitro release rates were determined by placing the implants in 20 mLof phosphate buffered saline pH 7.4 maintained at 37° C. for 3 hours.The concentration of 2ME2 in the vial was determined by HPLC and therelease rates of drug from the implants were recorded as μg/day(microgram/day).

Results:

The release rates for the different implant designs are shown in FIG.15. FIG. 16 tabulates the results. As was demonstrated, dual modereservoir implants representing this invention can be manufactured torelease predictable loading and maintenance doses. Using the delay incure technique effectively loads the surrounding silicone for the bursteffect and changing the thickness of the silicone coating surrounding a2ME2 drug pellet can alters the maintenance release rate of the implant.Design B was chosen for the rabbit studies, described in Example 7infra, because of its superior durability, optimal release rate, anddesirable life span.

EXAMPLE 7

To evaluate the feasibility of using the implants of this invention forhuman diseases, such as choroidal neovascularization, rabbit studieswere performed using 2ME2 intravitreal implants. Drug extractiontechniques were done to assay the ocular drug levels following theinsertion of these implants in the vitreous cavity. The ocular toxicityof these implants were evaluated by electroretinography (a test ofretinal function) and histopathology.

2ME2 powder was obtained from EntreMed Inc., Rockville, Md. For thisstudy, we chose a dual mode reservoir implant of Design B releasing 2ME2as described in Example 6.

Ocular Drug Levels:

Seven rabbits had 2ME2 implants (Design B) surgically placed in thevitreous cavity of the right eye as follows: All procedures on animalswere performed in accordance with protocols approved by the Animal Careand Use Committee. Male and female New Zealand white rabbits, weighing2-3 kg were anesthetized with intramuscular ketamine (35 mg/kg) andxylazine (5 mg/kg). One drop of proparicaine (1%) was placed in theinferior fornix for topical anesthesia, and the pupils were dilated with1 drop of phenylephrine hydrochloride (2.5%) and topicamide (1%). Usingsterile procedures, a lid speculum was placed in the right eye, and afornix-based conjunctival flap was made in the superotemporal quadrant.A 4 mm sclerostomy was made 3 mm posterior to the surgical limbus. Thedrug implant was inserted through the incision into the vitreal cavity.Prolapsed vitreous was excised as needed using a weck cell vitrectomytechnique. The sclerostomy was closed using 8-0 nylon and theconjunctiva was reapproximated to the limbus using 10-0 vicryl. The eyewas injected with balanced salt solution as necessary to normalize theintraocular pressure. Indirect ophthalmoscopy was done to confirmplacement of the implant in the vitreal cavity. Bacitracin ophthalmicointment was applied twice daily for three days.

Four rabbits were sacrificed at 1 month post-implantation and 3 rabbitsat 3 months. The right eye of each rabbit was removed and the tissuesprocessed for 2ME2 drug levels. Following enucleation the eyes werefrozen at −80° C. in order to prevent drug redistribution. The drugextraction procedure was as follows: the eyes were dissected whilefrozen and an equal weight of acetonitrile was added to extract the drugfrom the aqueous humor, vitreous humor, and blood. The specimens weresonicated, centrifuged, and the drug levels in the supernatantdetermined by HPLC.

Ocular Toxicity Testing:

The details of the electroretinography procedure in rabbit is describedin Example 4. Six NZW rabbits had 2ME2 implants (Design B) surgicallyplaced in the vitreous cavity of the right eye (OD) and a sham implantin the left eye (OS). The rabbits had their eyes examined clinically andserial electroretinography (ERG) performed to assess for drug toxicityover a 6 month period. The rabbits were sacrificed at 6 monthspost-implantation and their eyes were processed for histopathology. Theresults are summarized below.

Ocular and Blood Drug Levels:

The 2ME2 levels in the vitreous humor, the tissue that has intimatecontact with the retina, were in the therapeutic range for the controlof angiogenesis (see FIG. 17). There was no detectable level of 2ME2 inthe blood.

Ocular Toxicity:

The electroretinograms showed no abnormalities over the 6 month period.The clinical examinations and histopathology showed no signs of oculartoxicity.

Results:

The 2ME2 levels in the vitreous treated with implants representing thisembodiment of the invention are potentially therapeutic levels to treatchoroidal neovascularization. Since there were no detectable drug levelsin the blood of these rabbits, the risk of systemic toxicity from drugreleased by the ocular implant are negligible.

EXAMPLE 8

A study was performed to compare the efficacy in a rat model ofchoroidal neovascularization (CNV) of triamcinol one acetonide (TAAC) inintravitreal matrix implants of this invention to a comparison implant.

Methods:

Implant design:

Design A1: (comparison reservoir design):

A compressed TAAC pellet (0.5 mm diameter at 120 lb-force) was coatedwith medical grade silicone (final implant dimensions 1×2.5 mm).

Design B1: (single mode matrix design according to this invention):

TAAC dry powder was premixed with 0.05% HPMC then mixed with a 20%polyvinyl alcohol (PVA) solution to produce a 5% (by dry weight) TAACmatrix suspension (see example 2 for details). The suspension was pouredonto a glass plate producing a thin film, dried at room temperature, andcut into 1×1×2.5 mm sections, each section representing one matriximplant.

In-vitro release rates were determined by placing the implants in PBSand assaying drug concentrations over time with HPLC.

CNV Model:

To induce experimental CNVM formation, a series of 8 laserphotocoagulation sites were concentrically placed around the optic disk(of 1 eye) followed by surgical placement of either a Design A1, DesignB1, or sham implant (3 animals minimum in each group). The surgicalprocedure for implant insertion was similar to that in Example 5. At 35days, the eyes were enucleated, fixed in formalin and embedded inmethacrylate-JB4. The eyes were sectioned in the area of injection,counterstained with H&E and examined with a light microscope forchoroidal neovascularization. The CNVM at each laser burn was quantifiedby measuring the thickness and the mean value for each eye was recorded.

Results:

In vitro release rates:

Design A1 followed constant release kinetics and the release was1.96±1.73 μg/day over a 28 day period.

Design B1 followed first-order kinetics with an initial release rate of42.88±1.24 μg/day over the initial 48 hours; decreasing to 1.94±1.46μg/day by day 28. These results are graphically shown in FIG. 18.

CNV Model:

In the eyes with the sham implants, CNV development was very rapid andoccurred at 3-7 days after lesion induction and was sustained over 4weeks. The mean CNVM thickness at 35 days with the sham implant (nodrug) was 55±10 μm. The mean values for eyes with Design A implant was35-50 μm; Design B implant, 15-20 μm.

Results:

These results demonstrate that Design B1, a single mode matrix designrepresenting an embodiment of this invention, was more effective insuppressing CNV in a rat laser model compared with a comparativereservoir device representing the prior art. Design B1 implantsdelivered a large loading dose of drug that may be more effective forthe treatment of CNV than the low dose delivery of implant representingthe prior art. Most effective for human may be a loading dose of anangiostatic steroid followed by a low dose maintenance delivery topromote dormancy of the lesion over time. However, rat models of CNVonly last 4-5 weeks and these dual mode implants cannot currently beassessed adequately.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

What is claimed is:
 1. An ocular implant providing sustained-release ofa first therapeutic agent to the eye for a prolonged period of time,comprising: a composite material matrix layer including: (i) a firsttherapeutic agent, (ii) a polymeric matrix material into which the firsttherapeutic agent is dispersed, including (1) a bioerodible polymerpermeable to the therapeutic agent, the permeable polymer beingsuperhydrolyzed polyvinyl alcohol, and (2) a water-soluble polymerhaving greater water solubility than the permeable polymer, thewater-soluble polymer being a cellulose ether polymer, and (iii) adiscrete solid core containing the first or a second therapeutic agent,the therapeutic agent being dispersed, and the solid core being embeddedwithin the composite material matrix layer.
 2. The implant according toclaim 1, wherein the composite material matrix layer comprises about 5to about 50 wt % of the permeable polymer, about 0.05 to about 90 wt %of the water-soluble polymer, and about 1.0 to about 50 wt % of thefirst therapeutic agent.
 3. The implant according to claim 1, whereinthe composite material matrix layer comprises about 5 to about 50 wt %of the superhydrolyzed polyvinyl alcohol, about 0.05 to about 90 wt % ofthe cellulose ether polymer, and about 1.0 to about 50 wt % of the firsttherapeutic agent.
 4. The implant according to claim 1, wherein thecellulose ether polymer comprises hydroxyalkyl cellulose.
 5. The implantaccording to claim 1, wherein the cellulose ether polymer compriseshydroxypropyl methyl cellulose.
 6. The implant according to claim 1,wherein a part of the exterior surface area of the composite materialmatrix layer is covered by polymethyl methacrylate sufficient to adjustthe rate of delivery of the therapeutic agent from the implant to theeye.
 7. The implant according to claim 1, wherein the composite materialmatrix layer comprises about 5 to about 50 wt % superhydrolyzedpolyvinyl alcohol.
 8. The implant according to claim 1, wherein thetherapeutic agent is selected from the group consisting of antibioticagents, antibacterial agents, antiviral agents, anti-glaucoma agents,antiallergenic agents, anti-inflammatory agents, anti-angiogenesiscompounds, antiproliferative agents, immune system modifying agents,anti-cancer agents, antisense agents, antimycotic agents, myotic agents,anticholinesterase agents, mydriatic agents, differentiation modulatoragents, sympathomimetic agents, anaesthetic agents, vasoconstrictiveagents, vasodillatory agents, decongestants, cell transport/mobilityimpending agents, polypeptides and protein agents, steroidal agents,carbonic anhydrase inhibitor agents, polycations, polyanions,lubricating agents, and mixtures thereof.
 9. An ocular implant providingsustained-release of a therapeutic agent to the eye for a prolongedperiod of time, comprising: (a) a composite material matrix layerincluding: (i) a first therapeutic agent, and (ii) a polymeric matrixmaterial into which the first therapeutic agent is dispersed, includingpoly(ethylene vinyl) acetate and a cellulose ether polymer, and (b)optionally, a discrete solid core containing an additional amount of thefirst therapeutic agent or a second different therapeutic agent, whereinsaid solid core being embedded within the composite material matrixlayer.
 10. A method of delivering a therapeutic agent to an eye in needof treatment thereof, comprising attaching an implant containing atherapeutic agent to the eye, wherein the implant comprises a compositematerial matrix layer including a therapeutic agent, and a polymericmatrix material into which the therapeutic agent is dispersed includinga superhydrolyzed polyvinyl alcohol permeable to the therapeutic agentand a cellulose ether polymer, and, optionally, a discrete solid corecontaining additional therapeutic agent and embedded within thecomposite material matrix layer, effective to deliver the therapeuticagent to the eye.
 11. The method of claim 10, wherein the implant isattached to a subconjunctival region of the eye.
 12. The method of claim10, wherein the implant is attached to an intravitreal region of theeye.
 13. The method of claim 10, wherein the discrete solid core isincluded, and delivery of the therapeutic agent proceeds as an initialloading dose delivery followed by sustained release of a lower,relatively constant rate of infusion.
 14. The method of claim 10,wherein the therapeutic agent in the composite material matrix layer andthe discrete solid core comprises cyclosporine.
 15. The method of claim12, wherein the implant is attached to a subconjunctival region of theeye, and wherein therapeutic agent is delivered in an amount effectivefor corneal allograft therapy.
 16. The method of claim 10, wherein thetherapeutic agent in the composite material matrix layer and the pelletcomprises 2-methoxyestradiol.
 17. The method of claim 12, wherein theimplant is attached to an intravitreal region of the eye, and whereintherapeutic agent is delivered in an amount effective for treatment ofchordial neovascular membranes CNVM.
 18. The method of claim 10, whereintreatment is performed on the eye of a mammalian organism.